Nanostructure and photovoltaic cell implementing same

ABSTRACT

Nanostructures and photovoltaic structures are disclosed. A nanostructure according to one embodiment includes an array of nanocables extending from a substrate, the nanocables in the array being characterized as having a spacing and surface texture defined by inner surfaces of voids of a template; an electrically insulating layer extending along the substrate; and at least one layer overlaying the nanocables. A nanostructure according to another embodiment includes a substrate; a portion of a template extending along the substrate, the template being electrically insulative; an array of nanocables extending from the template, portions of the nanocables protruding from the template being characterized as having a spacing, shape and surface texture defined by previously-present inner surfaces of voids of the template; and at least one layer overlaying the nanocables.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/710,097 filed Aug. 22, 2005, and which is hereinincorporated by reference. This application also claims priority to U.S.Provisional Patent Application Ser. No. 60/710,262 filed Aug. 22, 2005,and which is herein incorporated by reference.

FIELD OF INVENTION

This invention pertains generally to nanotechnology and particularly tonano-scale structures and processes for making these structures.

BACKGROUND

Solar panels that harness solar energy and convert it to electricalenergy are well known. A typical solar electricity system includes thefollowing components solar panels, charge controller, inverter, andoften batteries. A typical solar panel, often referred to as aphotovoltaic (PV) module, consists of a one or more interconnected PVcells environmentally sealed in protective packaging consisting of aglass cover and extruded aluminum casing.

The PV cell ma be a p-n junction diode capable of generating electricityin the presence of sunlight. It is often made of crystalline silicon(e.g., polycrystalline silicon) doped with elements from either group 13(group III) or group 15 (group V) on the periodic table. When thesedopant atoms are added to the silicon, they take the place of siliconatoms in the crystalline lattice and bond with the neighboring siliconatoms in almost the same way as the silicon atom that was originallythere. However, because these dopants do not have the same number ofvalence electrons as silicon atoms, extra electrons or “holes” becomepresent in the crystal lattice. Upon absorbing a photon that carries anenergy that is at least the same as the band gap energy of the silicon,the electrons become free. The electrons and holes freely move aroundwithin the solid silicon material, making silicon conductive. The closerthe absorption event is to the p-n junction, the greater the mobility ofthe electron-hole pair.

When a photon that has less energy than silicon's band gap energystrikes the crystalline structure, the electrons and holes are notmobilized. Instead of the photon's energy becoming absorbed by theelectrons and holes, the difference between the amount of energy carriedby the photon and the band gap energy is converted to heat.

While the idea of converting solar energy to electrical power has muchappeal, conventional solar panels have limited usage because theirefficiencies are generally only in the range of 15% and are manufacturedusing costly silicon wafer manufacturing processes and materials. Thislow efficiency is due in part to the planar configuration of current PVcells, as well as the relatively large distances between the electrodesand the P-N junction. Low efficiency means that larger and heavierarrays are needed to obtain a certain amount of electricity, raising thecost of a solar panel and limiting its use to large-scale structures.

The most common material for solar cells is silicon. Crystalline siliconcomes in three categories; single-crystal silicon, polycystallinesilicon, and ribbon silicon. Solar cells made with single ormonocrystalline wafers have the highest efficiency of the three, atabout 20%. Unfortunately, single crystal cells are expensive and roundso they do not completely tile a module. Polycrystalline silicon is madefrom cast ingots. They are made by filling a large crucible with moltensilicon and carefully cooling and solidifying them. The polycrystallinesilicon is less expensive than single crystal, but is only about 10-14%efficient depending on the process conditions and resultingimperfections in the material. Ribbon silicon is the last major categoryof PV grade silicon it is formed by drawing flat, thin films from moltensilicon, and has a polycrystalline structure. Silicon ribbons efficiencyrange of 11-13% is also lower than monocrystalline silicon due to moreimperfections. Most of these technologies are based on wafers about 300μm thick. The PV cells are fabricated then soldered together to form amodule.

Another technology under development is multi junction solar cells,which is expected to deliver less than 185% efficiency in actual use.The process and materials to produce multifunction cells are enormouslyexpensive. Those cells require multiple gallium/indium/arsenide layers.The best is believed to be a sextuple-junction cell. Currentmultijunction cells cannot be made economical for large-scaleapplications

A promising enabler of PV cells and other technology is nanotechnology.However, one problem with implementing nanotechnology is that the minuteconductors may not be able to withstand their own formation, much lesssubsequent processing conditions or conditions of use in the endproduct. For example, the metal forming the nanoconductors may be soft,making it prone to bending or breaking during application of additionallayers.

Further, it has heretofore proven difficult and even impossible tocreate nanoarrays having structures of uniform size and/or spacing.

Thus, as alluded to, the technology available to create PV cells andother electronic structures is limited to some extent by processinglimitations as well as the sheer fragileness of the structuresthemselves.

Therefore, it would be desirable to enable creation of nanostructureshaving high aspect ratios and yet are durable enough for practical usein industry.

It would also be desirable to enable fabrication of a solar cell thathas a higher than average efficiency, and in some embodiments, higherthan about 20%.

SUMMARY

A photovoltaic structure according to one embodiment of the presentinvention includes an array of photovoltaic nanostructures, and aphotovoltaic device, the photovoltaic device being at leastsemi-transparent. The array is positioned relative to the photovoltaicdevice such that light passing through the photovoltaic device strikesthe array.

Various configurations are contemplated. In one aspect, the array ofphotovoltaic nanostructures is arranged in a brush configuration. Axesof the photovoltaic nanostructures may be tilted from a direction normalto the array. In another aspect, the photovoltaic device is a planarphotovoltaic structure.

In a further aspect, the photovoltaic device is a second array ofphotovoltaic nanostructures. The first and second arrays of photovoltaicnanostructures may be arranged in a brush configuration, wherein aheight of the photovoltaic nanostructures in the first array isdifferent than an average height of the photovoltaic nanostructures inthe second array in one embodiment, the photovoltaic nanostructures ofthe first array have the same composition as the photovoltaicnanostructures of the second array. In another embodiment, thephotovoltaic nanostructures of the first array have a differentcomposition than the photovoltaic nanostructures of the second array.For example, the photovoltaic nanostructures of the first array maycomprise an organic material, wherein the photovoltaic nanostructures ofthe second array comprise inorganic materials. In another example, thephotovoltaic nanostructures of the first array comprise, inorganicmaterials, wherein the photovoltaic nanostructures of the second arraycomprise inorganic materials.

The nanostructures of the second array may be coated with at least onehigh hands material, and the nanostructures of the first array arecoated with at least one low bandgap material.

A nanostructure according to one embodiment of the present invent onincludes an array of nanocables extending from a substrate, the array ofnanocables being formed using a template, an insulating layer extendingalong the substrate, and at least one layer overlaying the nanocables.

The nanocables may be elongated.

The template may be partially removed. At least a portion of thetemplate may form the insulating, layer.

The nanocables may have substantially uniform peripheries.

The template may be a membrane.

The at least one layer may be electroplated, may be formed by chemicalvapor deposition and etching, etc.

A nanostructure according to yet another embodiment of the presentinvention includes a nanocable having a rough outer surface and a solidcore.

A method for creating a nanostructure according to yet anotherembodiment of the present invention includes depositing material in atemplate for forming an array of nanocables, removing the template,forming an insulating layer between the nanocables, and forming at leastone layer over the nanocables. The at least one layer may be formed byelectroplating. The at least one layer may be formed by chemical vapordeposition, while etching may be used to expose the insulating layer.The at least one layer may create a photovoltaically active p-njunction.

A method for creating a nanostructure according to yet anotherembodiment of the present invention includes depositing material in atemplate for forming an array of nanocables, removing only a portion ofthe template such that the template forms an insulating layer betweenthe nanocables, and forming at least one layer over the nanocables. Theat least one layer is formed by electroplating, chemical vapordeposition, etc. The at least one layer may create a photovoltaicallyactive p-n junction.

A method for creating a nanostructure according to yet anotherembodiment of the present invention includes depositing material in atemplate for forming an array of pillars, removing the template, formingat least one layer over the pillars such that the pillars are covered bythe at least one layer, and depositing a metal contact over the at leastone layer such that the at least one layer is covered by the metalcontact.

A method for creating a reinforced nanostructure according to yetanother embodiment of the present invention includes forming a nanotubeof a first material in a template, forming a nanocable of a secondmaterial in the nanotube, and at least partially removing the template.Preferably, the first material is more rigid than the second material.Also preferably, the first material has a higher heat resistance thanthe second material.

A method for creating a reinforced nanostructure according, to yetanother embodiment of the present invention includes forming a nanotubeof a first material in a template, forming a nanocable of a secondmaterial in the nanotube, removing the nanotube from between thetemplate and the nanocable, depositing a reinforcing layer between thetemplate and the nanocable, and at least partially removing thetemplate.

A method for creating an array of nanotubes having a defined widthperpendicular to an axis thereof according to yet another embodiment ofthe present invention includes forming a nanotube of a polymericmaterial in a template, forming a nanocable of a second material in thenanotube, at least partially removing the template, and at leastpartially removing the polymeric material.

A method for creating a nanocable with a rough outer surface accordingto yet another embodiment of the present invention includes plating athin film of metal over the surface of a metallic nanocable such thatthe metal forms alloys with the nanocable at the surface of thenanocable, and removing the metal from the surface of the nanocable,wherein the outer surface of the nanocable is rough upon removal of themetal.

A method for creating a nanocable through etching a membrane on aconductor according to yet another embodiment of the present inventionincludes depositing material in a template for forming: an array ofnanocables, removing the template, forming an insulating layer betweenthe nanocables, and forming at least one layer over the nanocables.

Thus, one embodiment of the invention includes a method of formingconductive hanostructures. The method allows a precise control of radialand vertical dimensions of the conductive core and semiconductorcoating(s). The resulting nanostructure is known as a nanocable. Withthe method, nanocable arrays can be molded into any number ofgeometries, and then made rigid. Nanocable arrays may be made flexible,if desired. Nanocable arrays made according to the invention haveimproved electrical junctions, improved reliability, and improvedperformance.

In another aspect, the invention is a PV structure that overcomes manylimitations of current PV cell designs. With the PV cell disclosedherein, all photon absorption events occur near the p-n junction formaximum efficiency. Light is diluted up to several orders of magnitudeto reduce hot spots throughout the cell. The design can reduce backreflection of photovoltaic cells to less than 1%, and reduces thequantities of scarce materials needed to produce a photovoltaic cell.Nanocable semiconductor layers ma be tuned to be spectrally selective ofdifferent light wavelengths to further increase performance. Thus, thePV cell overall reduces the cost unit area for most photovoltaicmaterials and increases high output industrial power.

In yet another aspect, the invention is a method of enhancing thestructural soundness of a nanocable structure having a metal nanocable.Where the nanocable is made of a “soft” metal such as gold or copper,the nanocable ma be coated with a harder metal or compound forstructural reinforcement. Metals can also be deposited as alloys toincrease the hardness of the nanocable.

The invention according to another embodiment includes a method of usingorganic polymer thin films to precisely control the dimensions of ananocable. One or more organic polymer thin films may be deposited onthe inner wall of a pore in a membrane that is used to produce thenanocable, so that when the nanocable material fills the remaining spacein the pore, its dimensions will be precisely controlled by thethickness of the polymer layers.

The invention according to another embodiment includes a method offorming nanoporous nanostructures. Using surface alloying, nanostructuresurface may be changed from smooth to rough. Nanoporous or nano-roughnanostructure obtained by this method is more robust because thenanoporous layer is confined to a few monolayers in the surface (not theentire bristle volume) and still maintains a plain metallic core.

In another aspect, the invention is a method for creating an integratednanostructured device—the nanocable array—where the individualelements—the nanocables—are insulated from one another. Each individualstructure is a singular device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary solar brush that may beused to implement solar panels with improved efficiency.

FIG. 2 is a side cross-section of the solar brush.

FIGS. 3A and 3B are cross-sectional views of embodiments of the solarbrush having a layered structure.

FIG. 3C is a cross-sectional view of a solar brush embodiment employinga thin film planar device as a filter.

FIG. 4 is a top view of the solar brush showing the tops of thebristles.

FIGS. 5A-5H illustrate an exemplary method for fabricating the solarbrush.

FIGS. 6A-6F illustrate an alternative method for fabricating the solarbrush,

FIGS. 7A-7H illustrate a hard-metal reinforcement process that may beused to strengthen fragile nanocables.

FIG. 8 is a flowchart summarizing the steps of the hard-metalreinforcement process of FIGS. 7A-7H.

FIGS. 9A-9H illustrate a dimension-controlling process for forming thenanocables.

FIG. 10 is a flowchart summarizing the steps of thedimension-controlling process of FIGS. 9A-9H.

FIG. 11A-11I illustrate the carbon jacket process for producing organicnanocables.

FIG. 12 is a flowchart summarizing the steps of the carbon jacketprocess of FIGS. 11A-11I.

FIG. 13 A-E: illustrates the insulator etching process.

FIG. 14 shows the solar brush encapsulated in an optical casing forprotection.

FIG. 15 is a graph showing a potential power generation for a planarsolar cell.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

The following description is the best mode presently contemplated forcarrying, out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each and any of the various possiblecombinations and permutations.

Embodiments of the invention are described herein in the context ofsolar cells. However, it is to be understood that the particularapplication provided herein is just an exemplary application, and thenanocable arrangement of the invention is not limited to the applicationor the embodiments disclosed herein.

This disclosure also relates to nano arrays of thin film solar cells.Solar modules constructed using thin film systems tend to use a singlelarger single plane thin films solar cell, rather than an array ofsmaller interconnected nano-scale solar cells. The entire module can usea laser scribe to mark individual cells, h is important to note nanosystems will be processed differently than current technology thin tims. Four main thin film material system types are amorphous silicon(A-Si), copper indium selenide (CuInSe₂ commonly referred to as CIS),copper indium gallium selenide (CuIn_(x)Ga_(1-x)Se_(x)) commonlyreferred to as CIGS), and CdTe/CdS. A-Si films are typically fabricatedusing plasma enhanced chemical vapor deposition (PE-CVD).

The term “nanocable” denotes any donated body whose one dimension (e.g.diameter or width) is of nanoscale size and the other dimension islarger, potentially much larger. A nanocable may be fabricated withdissimilar materials, either as a core rod or wire that is laterallyenveloped by one or more layers of material(s), as a nanotube that isfilled with one or more layers of material(s), or as a single structureof one material. Nanocables are also referred as nanorod s or nanowiresor filled nanotubes. The flinch on al element of the nanocable in eachcase is the interface(s) between the two (or more) materials. In variousalternative configurations and modes of growth, a succession of layersof different materials, alternating materials or different thicknessesof materials can be deposited to form nested cylinder nanocables.

The term “photovoltaically active p-n junction” denotes any p-n junctionwith an adequate p-layer and n-layer thickness to generate electricity.

FIG. 1 is a perspective view of an exemplary solar brush 10 that may beused to implement solar cells with improved efficiency. As shown, thesolar brush 10 has a substrate 12, a first conductive layer 14, aninsulator layer 16, a second conductive layer 18, and a plurality ofbristles 20. Although the bristles 20 are shown to becylindrically-shaped in the particular embodiment, they may be of anyother shape including but not limited to cones, rectangular, domes, ormore complex geometries such as branched bristles etc. Each of thebristles 20 has a nanocable extending through its center, and layers ofsemiconductor around the nanocable. Bristles may protrude verticallyfrom the substrate or may protrude at angles. Bristles protruding atangles may increase the amount of semiconductor materials exposed to thesun when the sun is directly overhead and may improve internalreflections. Bristles can be modified to be smooth or hairy. Hairbristles may improve light absorption efficiency by further increasingthe surface area or improving internal reflections. Various shapes canbe obtained using asymmetric pore membranes. One or more electricallyconductive strips 33 may extend across the array or portion thereof toassist in carrying electricity away from the array, thereby improvingthe overall efficiency of the brush. The efficiency gains are morepronounced in larger arrays. Such strips 32 are preferably very thin toblock minimal light.

FIG. 2 is a side cross-section of the solar brush 10 with a metalnanocable. As shown, each of the bristles 20 has a nanocable 22extending through its core. The allocable 22 is typically a p-layerconductor, and extends through the insulating layer 16 to electricallyconnect with the first conductive layer 14. A p-type semiconductivelayer 24 of a sufficient thickness surrounds the nanocable 22, and ann-type semiconductive layer 26 of sufficient thickness is coated on thep-type semiconductive layer 24 to create a photovoltaically active p-njunction in each of the bristles 20. An n-layer conductor is depositedon the tops of the bristles 20 and the insulating layer 16 to form thesecond conductive layer 18.

The closer the photon absorption event is to the p-n junction, the morelikely the event will result in usable electricity. In the case of ananobrush, a reflective back contacting layer is not required becausethe photon can continue along the linear path so that it can contact thematerial on the opposite side of the cell thereby achieving a doublepass in each nanobristle, in FIG. 2, five cylindrical shell solar brushPV cells are shown. Thus, if the photon passes slightly off-center ofthe shell it has the potential to come into contact with as many as theequivalent of 10 p-type layers (the layer where the solar event takesplace) in this brush design. If the p-layer conductor is sufficientlysmall most of the photons will pass through five thicker layers, in theactual case, the solar brush, with millions of bristles per cm², wouldeffectively approach the efficiency of 100% of all usable photon energy.

The substrate 12 may be a conductive material or a nonconductivematerial (coated with a conductive material), rigid or flexible. Forexample, the substrate 12 could be glass, doped silicon, diamond, metal,polymer, ceramics, or a variety of composite materials. Thin metal foilor certain polymers can be used where flexibility is desired. Structuralintegrity of the nanocable will vary with material choices. In the caseof brittle or easily deformable bristles, a flexible substrate materialcould be used if attached to a rigid or semi-rigid surface. The moldedsurface/flexible membrane may be of particular help when PV cells aredesired for an aerodynamic surface such as an airplane part, the roof ofa car, the surface of other vessels or portable devices.

Each of the bristles 20 is a discrete nanoscale PV cell. Compared toconventional flat PV cells design where only a single “xy” planarsurface is exposed to light, the solar brush 10 has an “xyz” or athree-dimensional surface. Thus, for a given volume, the solar brush 10has a useful surface area that can be several times to thousands oftimes greater than the “xy” surface area of conventional PV cells. Thearea between solar bristles 20 could be sufficiently wide as to make thebrush absorptive to the majority of photons. Additionally, the bristlesmay be thin enough to be partially transparent. This effectivetransparency and bristle spacing would increase effective energygeneration to happen from sunrise to sunset while flat PV cells workoptimally when the sun is straight above the PV surface. Because theeffective energy generation from the solar brush is expected to be manytimes higher than conventional PV cell technology, the weight perkilowatt generated would be many times lower. This would allow use insmall applications such as charging electronic devices (cell phone,computer, PDA, etc.), use in medium scale applications such as lightweight roof-top energy for industrial and agricultural power generation,and use in large applications such as a light weight energy source fortransportation (automobile, aircraft, barges). The efficiency of thecell would also enable improved power generation in low lightconditions. The wide range of spectrum adsorption may also generatepower from infra-red light at night time. Another advantage of usingnanocable structures is that the p-n junction associated with eachnanocable has a smooth interface that results in a sharper junction. Thesmoothness is improved at nanoscale as the roughness (measured asrms-root mean square for instance) increases as the scale increases.

It should also be noted that though the axes of the bristles 20 areoriented normal (perpendicular) to the plane of the array in thedrawings, the axes of the bristles may be tilted slightly (a few degreesfrom normal) or pronouncedly (e.g., 40-89 degrees). One reason why atilted configuration may be desirable is to reduce unimpeded penetrationof light into the array when the light is traveling in a directionnormal to the array.

FIG. 3A is a perspective view of the solar brush 10 having a layeredstructure. The structure in FIG. 3A has a layer A and a layer 13, witheach layer having a substrate 12 a, 12 b, the first conductive layer(not shown), the insulator layer (not shown), the second conductivelayer (not shown), and bristles 20 a, 20 b. In the layered structure,the substrates 12 a, 12 b, the first conductive layers, the insulatorlayers, and the second conductive layers of one or both layers may be atleast semi-transparent so that light can travel between the layers Aand/or B. When the solar brush 10 is layered, the bristles 20 do nothave to be as densely arranged as in the single-layer structure toachieve the same efficiency. The layered structure can be made usingcruder, and therefore less expensive, equipment than the single-layeredstructure with densely arranged bristles 20. Although the embodimentshown in FIG. 3A has two layers of approximately the same bristleheight, this is not a limitation of a layered brush structure.Photovoltaic cells with layered brush structures can contain as manylayers as desired to generate the desired efficiency and power.

The layered brush structure can also be used to increase photovoltaiccell efficiency by using a high- and low-band gap material andsemiconductor thicknesses tuned for spectral selection. A high band gapmaterial can be used to coat the upper photovoltaic brush, and the lowband gap material can be used to coat the lower photovoltaic brush. Theupper material would convert higher-energy light to electricity anddissipate much heat. The lower material could convert lower-energylight. This would increase both the efficiency and the life span of thelower brush A.

The layered structure does not need to be made of the same material orby the same process. For example, the upper brush could be producedusing a conductive/transparent core of silicone and a silicone substratemade from photolithography and chemical vapor deposition and the lowerbrush made with organic dye technology. This way, the low-band-gap lightcan easily pass through the upper layer and reach an organic nanocablebase. The base may be made from an anodized aluminum template, carbonnanojacket, and wet polymer process. The layers may or may not have thesame dimensions and/or composition. The design need not be limited totwo types of photovoltaic cells. A multitude of cells can be includedwith a multitude of photovoltaic materials so long as each cell hasadequate transparency for light to reach the cell below.

FIG. 38 is a side view of another layered structure wherein the averagebrush heights are different in the two layers. The embodiment of FIG. 3Billustrates that there can be structural differences between the twolayers.

FIG. 3C illustrates that a transparent thin film planar device can alsobe employed as a filter over a brush layer if desired.

Thin, minimal reflectance metals such as gold may be layered along withthe n- and p-layers to conduct the current so further gains inefficiency might be achieved.

One benefit over current technology is, as previously mentioned, thatthe maximum efficiency for a given material can be achieved. Anotherpotential benefit may be achieved by layering material with differentband gaps (energies required to excite electrons). The idea is to have ahigh band gap material such as GaAs (max efficiency ˜20%, band gap ˜1.4eV) or CdTe (max efficiency ˜30%; band gap ˜1.6 eV) at the tip of thebristle and a reduced band gap material further down the bristle such asCIS or CIGS type PV material further down (max efficiency of ˜24%, bandgap ˜0.8 eV). Photons with low energy will not react with high band gapmaterial but will be available to react with low band gap materialfurther down the bristle at further penetration depths. This could beachieved by CND of CIS material on a nanocable, followed by etching tothe top metal core of the nanocable, followed by catalytic growth on topof the nanocable, and the cable would be finished up by electroplatingof cdTe/CdS. The solar brush PV cell design could also be amultijunction cell and is a superior architecture for such.

A flexible nanopore substrate can be used as the substrate 12 fordeposition of metal. The substrate 12 could be a membrane applied to orconstructed on a thin conductive sheet, and may be made into any desiredshape. After metal deposition in the membrane pores occurs, the bristles20 are formed. While other PV tapes and films have XY flexibility andstrength, they are limited and no other technology allows for XYZ designof a rigid or flexible long lasting solar cell. The varied geometry ofthe solar brush allows the PV cells to be optimized for solar exposurefrom a fixed location, optimal aesthetic appeal, and minimal aerodynamicdrag for transportation applications. Specific geometries combined withreflective substrates can effectively produce a combined PV film andsolar concentrator.

There are many combinations of materials that may be used for the solarbrush 10. One configuration is to use a Si thin film. Otherconfigurations include CdTe/CdS (CdTe/CdS/SnO₂/Indium TinOxide(ITO)/glass), GaAs/GaInP, CuInGaSe₂, Cu(In_(x)Ga_(1-x))(S, Se)₂,CuIn_(1-x)Ga_(x)Se_(1-y)S_(y), CGSe/CdS, CuIn_(x)Ga_(1-x)Te₂/n-InSe.CdS/CIGS interface, ZnS/CIGS, Cu₂S—CdS, CuInS₂ or a mix of Cu_(x)S,CuInS₂ and CuIn₅S₈, Cu(In, Ga)Se₂/CdS, CIS/In₂Se₃, InN, CIS/In₂Se₃,ZnS_(x)Se_(1-x). GaInP/GaAs, GaInP/GaAs/Ge, GaAs/CIS, a-Si/CIGS (a-Si isamorphous Si/hydrogen alloy), FeS₂, Cu₂O, ITO/a-CNx (Al Schottkythin-film carbon nitride solar cells), and MoS₂ based solar cells ormore general: MX2 (M=Mo, W; X═S, Se) thin films with Ni and Cu additiveslayers may be used as well. An Al₂O₃ layer ma be used as a diffusionbarrier with the CuInGaSe₂ type PV cells. The manufacturing step mayinclude heat annealing at high temperatures to allow for theconsolidation of polycrystalline deposits to form a single crystalmaterial or improve the structural integrity and regularity or geometryof the materials. Alternatively, single crystalline growth of layersshould be favored by slow growth of the layers at moderate temperatures.Single crystalline deposits are important for optimum electron transportand photon absorption.

Deposition of the various materials can include chemical vapordeposition, solution phase deposition, electrochemical deposition,electrochemically induced sol gel deposition, electrochemical atomiclayer epitaxy, electroless deposition, e-beam evaporation, sol-gel withelectrophoresis or centrifugation, electron beam lithography, scannedprobe lithography, pressure injections, polymerization andelectropolymerization, and pyrolytic decomposition. Nanocables can alsobe grown from catalyst sites from chemical vapor deposition, wet or dryetched from a substrate, etc.

When designing a PV cell, one of the considerations is the photon flux.The number of photons that make it through the atmosphere at a givenpoint remains relatively constant regardless of modifications in the PVcell that receives them. When determining the appropriate geometry for aPV cell, it is convenient to start by calculating the area of the gapsand the area of the bristle-tops.

FIG. 4 is a top view of the solar brush 10 showing the tops of thebristles 20. Although the bristles 20 are shown to be arrangedregularly, this arrangement can be changed to suit the application. Thetops of the bristles 20 have a combined area of which is calculated asπ(D/2)²ρ wherein D is the diameter of the bristle and ρ is the cabledensity (number of cables/unit area). The total area (A_(total)) of thePV cell is W×L. The area of the gaps between the bristles can then becalculated using the following formula:

A _(total) =A _(top) +A _(gap)

During the same calculation, it is useful to determine if the spacingfor a given cable density is viable for given geometries. When thediameter of the nanocable 22 (D_(nanocable)) is 50 nm, the minimum PVbristle diameter D is about 220 nm. When D_(nanocable)=150 nm, theminimum PV bristle optical thickness is about 320 nm. The physicaldiameter of the bristles 20 will be 100-500 nm larger than the diameterof the nanocable 22, but these numbers should be used for the opticaldiameter calculations because the outer shell is transparent. Theoptical diameter is used for calculating the solar efficiency, and thephysical diameter is used for determining process limits.

One preferred density (ρ) range for nanocables is:

ρ=10⁶-10⁹ pores/cm²=10¹⁰-10¹³ poers/m²

when using track etched membranes. When using metal oxide templates thedensity range shifts to:

ρ=10¹²-10¹⁵ pores/m²

For the low density case, there is 1 cable per 10⁻¹⁰ m², or 1 cable inthe center of a 10⁻⁵×10⁻⁵ square, so the separation between the centerof cables is 10⁻⁵ m or 10000 nm. From that number, the diameter of thebristle from its center axis (which extends through the length of thenanocable 22) to the n-layer is subtracted. The spacing may not smallerthan the cable and is preferably larger, so cases involving unrealisticphysical spacing were eliminated from calculations in Table i. Opticalspacing, S, is given by the following:

S=cable separation(center pt. to center pt.)−diameter a bristle(semitransparent material)

After Optical spacing is determined, the areas of the top of the PVbristles (A_(top)) as well as areas between the bristles (A_(gap)) aredetermined. Table 1 shows that majority of the planar surface area lieswithin the gaps of the PV cell, not the bristle tops. However, there aredesign points that have significant levels of top surface area.

TABLE 1 Planar area calculations for the PV brush. A_(top) (m²) A_(gap)(m²) ρ (#/cm²) D (nm) S (nm) 3.00 × 10⁻⁴ 0.9996 10⁶ 220 9780 8.04 × 10⁻⁴0.9989 10⁶ 220 9680 3.80 × 10⁻² 0.9620 10⁸ 370 780 8.04 × 10⁻² 0.989210⁸ 370 680 1.90 × 10⁻¹ 0.8100 5 × 10⁸ 220 227

Planar area and mass per area are crucial to determine back reflection.For planar cells, reflection bounces much of the light out of the PVcell before it has a chance to be absorbed and generate electricity.However, back reflection can benefit the planar cell by bouncing thelight off of the back of the cell to give the cell two opportunities toabsorb photons from the same stream of light. However, while the backreflection increases the number of absorptive events in the planar cell,it also increases the amount of heat generated per unit volume. In thecase of the solar brush 10, only a fraction of the photons that hit thebristle tops can reflect away from the PV cell.

In many cases with the solar brush 10, over 96% of the light fills intoA_(gap). Several things happen to the light that falls into the gap: (a)the light is absorbed, (b) the light continues straight through thebristle into the next nearest bristle (as shown in FIG. 2), and/or (c)the light is reflected down into the solar brush at an angle ofreflection equal to the angle of incidence. In each case, the light fromthe gap continues into the bristle. The majority of the light is eitherabsorbed or continues straight through the brush. Back reflection is afunction of material thickness as well as material type. Because thesolar brush is made up of millions of thin bristles, they become nearly“transparent.” Thus, in every case except Θ=90° (where Θ is defined asthe angle of the sun relative to the plane of the PV cell substrate),back reflection is minimal. If it is assumed that 96% or greater lightfalls within the gap and each bristle has 90% transparency, then thereis a maximum of 0.04% back reflection.

The depth and areas of penetrated light are also calculated. This is ameasure of how uniformly the light can be dispersed throughout the PVbrush. The penetration of light is governed by the following formula:

T _(pen)=penetration thickness S=tan Θ

The thickness or bristle height is related to the maximum penetration.The average penetration for a light stream in many cases would be about0/2. However, as Θ approaches 90°, the bottom of the cell could betheoretically flooded with light. However, in reality, this floodingeffect is minimal or nonexistent because the light is affected byirregularities in the bristle geometry and can be eliminated by tiltingthe bristles slightly.

Table 2 shows how deep the light penetrates and what fractional area isused on a first pass by dividing T_(pen) by T, which is the totalbristle height. This is a measure of how much the initial light is beingdiluted. More dilute light leads to lower maximum temperatures or fewerhot spots in the cell, resulting, in improved overall efficiency.

TABLE 2 Penetration percentage for a T = 10 μm cell as a function of sunangle above the horizon Θ = 10° Θ = 45° Θ = 80° Θ = 90° SpacingPenetration Penetration Penetration Penetration (nm) (%) (%) (%) (%) 98017.24 97.8 100 100.00 9680 17.07 96.8 100 100.00 780 1.38 7.8 44.24100.00 680 1.20 6.8 38.56 100.00 227 0.40 2.27 12.87 100.00Penetration percentage for a 100 μm cell as a function of sun anglerelative to the plane of the PV cell substrate is simply 10 times lower.The penetration is an important design criteria. For transparent cables,if there is 10% penetration, the light will have as few as 10 passesthrough PV cables, and the average photon would have up to 2.0 passesthrough the p-n junction since the photon may pass through the p-njunction twice per bristle. It is probably best to set design criteriato target less than 2.0% for most of the day to insure adequateabsorption opportunities for the light stream. When Θ goes to 90°, tan Θgoes to ∞, temporarily making the penetration level 100%. Optimization,however, will be a function of field testing results.

The total PV absorption area is much greater for the sides of thebristles 20 than for the tops is the surface area available by PV brushwhich is given by:

A _(cell) =T(π)(Dρ/2)

where T is the height of the cable, D is the optical diameter of the PVbristle; and ρ is the number of bristles per unit area. The quantity isdivided by 2 because it is assumed that most light absorption will comefrom the sun which is shining on half of the cell at one time. Therewill be significant absorption events from scattered light as well, butthe majority of photons conic directly from the sun. Table 3 summarizessome calculations, and shows that the PV cell surface area increasesrapidly with denser cell spacing and bristle height, “Cell spacing” ismeasured from the center of one bristle to the center of its neighboringbristle.

TABLE 3 PV Brush Area Calculations PV Cable A_(cell) Cell HeightDiameter Density (m² Brush/m² Spacing (μm) (nm) (#/cm²) planar) (nm) 50220 10⁶ 0.17 9780 100 220 10⁶ 0.35 9780 50 220 10⁸ 17.28 780 100 220 10⁸34.56 780 50 220 5 × 10⁸ 86.40 227 100 220 5 × 10⁸ 172.80 227 50 320 10⁶0.25 9680 100 320 10⁶ 0.50 9680 50 320 10⁸ 25.13 680 100 320 10⁸ 50.27680

The penetration area is proportional to the penetration depth, as shownby the following formula:

A _(pen)=area initially penetrated by light=T _(pen)(π)(Dρ)

Where A_(gap)>>A_(top) the dilution of light is represented by thefollowing formula:

A _(pen) =T _(pen) /T*A _(total)

From A_(pen) and A_(gap) (Table 1), a calculation that shows the amountof light dilution that occurs in the cell can be made. The lightdilution is important to opportunities for solar absorption events anduniform heating. Wherever there are hot spots there is rapidly degradingconversion efficiency. Wherever there is concentrated light that tendsto create hot spots, the ratio of opportunities for an absorption eventto the number of photons decreases.

TABLE 4 Dilution levels for PV cells when the sun's angle is at 10°.Dilution PV Cable Cell (times Height Diameter Density Spacing original(μm) (nm) (#/cm²) (nm) area) 50 220 5 × 10⁸ 227 15.23 100 220 5 × 10⁸227 30.47 50 320 10⁸ 680 4.43 100 320 10⁸ 680 8.86

FIGS. 5A-5H illustrate an exemplary method for preparing the solar brush10 including a metal substrate and bristles of CdTe and CdS. As shown inFIG. 5A, a substrate is prepared by sonicating with ultra pure water(e.g., 18 MΩ) and ethanol in an alternating manner. For example, a metalsubstrate may be sonicated with ultra pure valor for 10 minutes, thenwith pure ethanol for 10 minutes, and this water-ethanol cleaning cyclemay be repeated two more times. If desired, the cycle may be performedmore or less than three times and/or art initial detergent-water,acid-water cleaning, or NaOH/NaCN/detergent electropolish process couldbe added. The type and amount of cleaning that is appropriate will be afunction of how clean the substrate 12 is to begin with and the type ofmaterial the substrate 12 is made of.

The substrate 12 may be a conductive material metal) or a nonconductivematerial (e.g., glass or polymer) that is coated with a conductivelayer.

FIG. 5B illustrates the substrate 12 coated with the first conductivelayer 14 that serves as the p-layer conductor in the PV cell. The firstconductive layer 14 may be any well-known conductive material deemedsuitable by a person skilled in the art, including but not limited togold, copper, nickel, molybdenum, iron, aluminum, doped silicon, andsilver. In one embodiment, a 500-nm layer of gold is evaporated on aglass substrate at 0.2 Å/s using an electron beam evaporator at apressure under 5×10⁻⁶ mbar at room temperature. In other embodiments,electroless plating is used with copper salts or Na₃AuSO₃ dissolved in50 mM H₂SO₄. After metallization of the substrate 12, the surface of thefirst conductive layer 14 is rinsed with ultra-pure water (e.g. for 1minute), rinsed with ethanol, and dried with nitrogen.

FIG. 5C illustrates a template 30 that may be used to form the bristles20. The template 30 may be a membrane or porous structure that can beconstructed on a conductive base, or the template 30 may be any of thecommercially available nano-porous or micro-porous membranes, such as,for example, those made by Whatman Corporation under the trade namesNucleopore®, Anodisc® or and Black Cyclopore®. Track-etched membranesthat have pore sizes in the range of 10 nm-5 μm are particularly useful.These track-etched membranes are typically made frompolyethyleneterephthalate (PET) or polycarbonate (PC). Membranes mayalso be partially etched to deliver conical nanocables. Conicalnanocables are thought to be significantly stronger than cylindricalnanocables but can be processed in a nearly identical way to thecylindrical nanocable. Selection of the membrane 30 depends on theparticulars of the PV cell that is being fabricated. Different pincombinations have different thickness requirements and thereforedifferent cable size requirements. Before electrochemical deposition,the membrane 30 is cleaned and air bubbles expelled from the pores bysubmerging the membrane 30 in methanol and sonicating for 5 minutes.

FIG. 5D illustrates the membrane 30 connected to the substrate 12 thathas been coated with the first conductive layer 14. There are a numberof ways to connect the membrane 30 to the conductive substrate 12 or themetallized nonconductive substrate 12. For example, a TiO₂ solution canbe used as a conductive glue to fix the membrane to the surfaces.Alternatively, the membrane can be fixed using a Radionics SilverConductive Paint®. Some substrates require no adhesion. The membrane issimply placed on top of the substrate provided there is good surfacecontact. Alternatively, the membrane could be attached to the surfacewith a clamp, using ultrasonic welding, or by fitting the surface andthe membrane into a jig.

FIG. 5E illustrates the deposition of metal 32 into the membrane 30 andon the substrate 12. In an illustrative plating process, a Sn sensitizeris applied to the membrane 30 through a 5 to 45-minute immersion in0.26M SnCl₂ and 0.07 M trifluoroacetic acid dissolved in a solventhaving a molar ratio of 1:1 methanol to water. The membrane is rinsedwith methanol. Sn adheres to the pore walls and outer surface of themembrane. Next, the membrane is immersed in an aqueous solution of 0.029M ammoniacal AgNO₃ for five minutes. This causes a redox reaction whereSn²⁺ is oxidized to Sn⁴⁺ and Ag⁺ is reduced to elemental A. Some silveroxide is also generated.

The pore walls and the membrane 30 become coated with discretenanoscopic Ag particles. The membrane is rinsed with ethanol andimmersed in water. Then the membrane is immersed in a 7.9 mMNa₃Au(SO₃)₂/0.127M Na₂SO₃/0.625 M formaldehyde solution that has atemperature of −0° C. Gold plating is continued for 10 to 24 hours (timeis dependant on pore size), at which time the nanocables are fullyformed in the membrane.

An alternative way to deposit materials inside membranes entails usingelectrophoresis or centrifugation sol-gel methods, electrochemicalatomic layer epitaxy, chemical vapor deposition, sputtering, E-beamevaporation, thermal evaporation, electron beam lithography, and scannedprobe lithography. Alternatively, well known additives can be dissolvedin the solution to impart nanocable strength or better electricalconnections to the n-layer conductor. Preferably, metal covers allexposed areas of the membrane, substrate, and fills the pores. After thegold deposition, the membrane is soak with water and rinsed 4 times overa 3-hour period and immersed in 25% nitric acid for 12 hours to removeresidual Sn or Ag. Finally, the membrane is rinsed with water and airdried. Evaporative metal deposition can also take place in the samemanner as in FIG. 5B. One advantage of electroless or electro-depositionis that it does not require a clean room or high temperatures to depositthe metal on the substrate.

Alternatively, the membrane may be placed into the electroless platingsolution by itself. The top, bottom, sides and pores become metallized.The membrane 30 may be glued as mentioned above to the metallizedsubstrate 12.

If desired, atomic layer epitaxy may be used to build a protective coverover the membrane 30. Atomic layer epitaxy may be used as an alternativeto electrochemical epitaxy.

FIG. 5F illustrates the removal of the membrane 30, leaving theconductive cables (nanowires) 32 attached to the substrate 12. Membraneremoval is most commonly done by solvent extraction. Partial membraneremoval is often desirable. Layered membranes make it easier to achieveuniform partial dissolution. Generally, dichloromethane is used to notonly remove the membrane but also the outer layer of metal leaving, thenanocables. In some cases, the top conductive surface may be removedusing ethanol to wipe out the excess after the membrane was coated butbefore it is immersed in 25% nitric acid. Tape can also be used toremove the outer metal, and may be used in conjunction with furthercleaning steps. In some cases, it is possible to physically peel themembrane off.

Alternatively, the membrane itself can have the metal pre-depositedtherein, or the metal can be deposited into the membrane prior tocoupling with the substrate. The metal will fill the pores and coat theouter surfaces of the membrane. The membrane can then be glued withtitanium dioxide or silver paste to the substrate prior to membranedissolution.

As shown in FIG. 5F, the membrane 30 may be dissolved until adequatematerial is left to act as the insulating layer 16. Alternatively, themembrane may be completely dissolved and an insulating layer depositedusing any suitable method such as spin coating, CVD, etc.

The insulating layer 16 may keep the current from the n-layer and playerfrom short circuiting. The insulator can also limit deposition of PVmaterial to the nanocables. Because insulation eliminates the effects ofdefects of one cable from affecting its neighbors, processes likeelectroplating become feasible.

Electroplating is a desirable process because of low equipment costs andrelatively good material conservation relative to other processes suchas sputtering and CVD which deposit material throughout the chamber inaddition to in the desired area. The thickness may easily be determinedby using various exposure times to dichloromethane and verifying themembrane thickness with scanning electron microscopy.

If all of the membrane 30 is removed, excessive material is consumed.This process may be used if a thinner insulating material or a materialother than the material the membrane 30 is made of is desired to formthe insulating layer 16 in this case, the desired material may bespin-coated on the substrate 12 with polymethylmethacrolate (PMMA) to athickness of about 1 μm. The PMMA may function as a membrane glue and/oran insulator. Any insulating, material that can be applied to the PVcell be it polymers, silicone dioxide, or any insulator that can haveadequate dimensional control during application. The PC membrane may beplaced on top of the PMMA and baked at around 100° C. for about an hour.

In some embodiments, the insulating layer is eliminated altogether. Aslong as to the p and n layers are adequately produced, direct contactwith the conducting layers is possible.

In other embodiments, holes are made in the insulating layer afterattachment of the membrane. For example, reactive ion etching (RIE) withoxygen and/or wet etching may be used to drill through the insulatinglayer 16 to allow the nanocables 32 to connect with the first conductivelayer 14.

In other embodiments, membrane can actually be used as a masking layerto etch pores in the underlayer, which is the insulating layer 15 inthis case.

FIG. 5G illustrates the deposition of a p-type semiconductive layer 24.Where the p-type semiconductor is CdTe, for example, the electrochemicaldeposition is done using 50 mM H₂SO₄+1 mM CdSO₄+0.1 mM TeO₂ solutionsdeoxygenated with nitrogen prior to use at room temperature. Thereference electrode may be Ag/AgCl/3 M NaCl and the counter electrodemay be a gold wire. Ultra-pure (e.g., 18 MΩ) water rinses are performedbetween deposition steps with nitrogen drying. A thin layer of Te may bedeposited to prevent Cd diffusion into the nanocable. When CdTe layer isdeposited in an electrochemical cell from a solution of 0.5M CdSO₄ and2.4×10⁻⁴ M TeO_(Z) in water at a pH of 1.6 at 90° C., the optimumdeposition potential for a stoichiometric film is −400 mV versus the Ptreference electrode. CdTe is also known to be deposited in ammoniasolutions. To deposition on the bristle surface can eliminate Cddiffusion into the core of the PV device. The CdTe layer also can bedeposited by ECALE (electrochemical atomic layer epitaxy). ALD (atomiclayer deposition in chemical vapor deposition system) or sol-gel. Whennon-electroplating processes such as CVD-related methods are used,etching can be used to remove the p-type layer 24 at the base of thestructure to expose the insulation layer and create isolation betweenthe nanostructures.

FIG. 5G also illustrates the deposition of an n-type semiconductivelayer 26. Where the n-type semiconductor is CdS. CdS deposition isperformed in 1.5 mM SC(NH₂)₂, 1.5 mM Cd SO₄, and 2 mM NH₄OH heated to atemperature of about 40-70° C. Under these conditions, a 4.5 minuteexposure would lead to a CdS layer of about 30 nm. The CdS layer alsocan be deposited by ECALE (electrochemical atomic layer epitaxy), ALD(atomic layer deposition in chemical vapor deposition system) orsol-gel. Again, when non-electroplating processes such as CVD-relatedmethods are used, etching can be used to remove the p-type layer 24 atthe base of the structure to expose the insulation layer and createisolation between the nanostructures.

FIG. 5H illustrates the deposition of the second conductive layer 18that completes the PV circuit. The second conductive layer 18 may beadded using atomic layer epitaxy. This deposition connects the secondconductive layer to the base of the n-conductors without contacting thenanocable. Alternatively, a thin layer of electroless metal can becoated as in the process illustrated in FIG. 5B as long as the metalremains thin enough to maintain adequate transparency. Vet anotheralternative is to apply a transparent conductive polymer such aspoly(3-hexylthiophene) (P3HT),poly[2-methoxy,5-(2-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV),poly (phenylene vinylene) (PPV), and polyaniline to the outside of thenanocables to complete the circuit. The polymer could also provideadditional structural support. Since the PV circuit is built on thenanoscale, penetration of the polymer may be challenging. For thisreason, thinner solutions may be preferred. However, exposing the uppersurface of the PV cell would provide adequate conduction. Preferredpolymers are light and oxygen stable. Many different conductive polymersare useful to make the electrical contacts and are described in T. A.Skatherin, Handbook of Conductive Polymers 1, which is incorporated byreference in its entirety.

Additionally, gel electrolytes may be used to make the electricalcontact for the n-layer as shown in US200410025933, which is hereinincorporated by reference. The electrolyte solution could be acombination of poly(4-vinylpyrimidine), poly(2-vinylpyrimidine),polyethylned oxide, polymthanes, polyamides and a lithium salt. The saltcould be lithium iodide, lithium bromide, lithium perchlorate, lithiumthiocyanate, lithium trifluormethyl sulfonate, and lithiumhexafluorophosphate to name a few.

Although FIGS. 5A through 5H illustrate an exemplary method offabricating the solar brush 10, there are many suitable variations ofthe process. For example, an organic photovoltaic material could beused. For example, PV cells could be made based on Dr. Michael Grätzeland co-worker's technology developed at the Swiss Federal Institute ofTechnology. The metallic core of the nanobristle could be made of metaloxides based on Ti, Zr, Sn, W, NB, Ta, and Tb. The cables can then becoated with an organic dye such as xanthines, cyaflines, mercocyanines,and phthalocianines, and pyrols. Many of these compounds have beentested by Konarka Corporation and have been developed for lowtemperature sintering as illustrated in patent application US2004/00259934. Fortunately, the nanocable eliminates the sinteringconcerns and allows the organic compound to be easily applied andefficiently used on the surface of the nanobrush.

Also, any membrane with micropores can be applied to the substrate 12 toproduce the PV brush. Also, any metal deposition should work withnanopores be it chemical vapor deposition, plasma vapor deposition,metal organic vapor deposition, electrochemical deposition(electrochemical epitaxy, under-potential deposition), liquid phaseepitaxy, molecular beam epitaxy, hot wail epitaxy, sputtering. E-beamand thermal evaporation, electroless deposition, chemical bathdeposition, sol gel and solution methods, vapor-liquid solid methods,sonochemistry methods, and microwave methods.

Nanoporous structures of certain metal oxides can be obtained with themetal anodization process instead of, or as a variation of, the methodillustrated in FIGS. 5A-5H. Among other systems, Al, Ti, and transparentconductive oxides can be anodically oxidized to form a regular nanoporestructure.

In one experiment, tin oxide was anodized. Before electro deposition, athin Au film was sputtered on one side of the aluminum anodicallyoxidized (AAO) membrane to serve as the conductive layer. Electrodeposition of Sn into the pores of the AAO membrane was carried out at aconstant current density of 0.75 mA/cm² for 1 hour in electrolytecontaining sodium tricitrate of 25 and tin dichloride of 7 g/L. The Snembedded in the AAO membrane was anodized at 0 V in 0.2 M boric acid,whose pH value was adjusted to 8.6 by 0.5 M NaOH(aq). The anodizationproceeded until the current density dropped to almost zero. The AAOmembrane was then removed through wet etching with 0.5 M. NaOH(aq),leaving behind an array of nanoporous tin oxide nanorods. Finally, thesamples were calcinated at 500° C. for 3 hours in air.

One embodiment of the present invention provides a method of formingnanoporous nanostructures. Using surface alloying, the nanostructuresurface may be in changed from smooth to rough. Nanoporous or nano-roughnanostructure obtained by this method is more robust because thenanoporous layer is confined to a few monolayers in the surface (not theentire bristle volume) and still maintains a plain metallic core.

To create a nanostructure with a rough outer surface, in one example, athin film of (e.g., a monolayer of) Cd can be deposited on the surfaceof the gold bristles mentioned above. Electrochemical deposition of Cdis performed in the under-potential region (at potentials more positivethan the Cd bulk deposition potential) for a few minutes and then the Cdlayer is removed by switching the potential to more positive values.Stripping the Cd layer leaves a rough Au surface behind. After exposureto corrosive materials, the Cd dissolves, leaving a ragged but sturdynanocabie with a solid core. Electrochemical deposition of Cd isperformed in the under-potential region (at potentials more positivethan the Cd bulk deposition potential) for a few minutes and then the Cdlayer is removed by switching the potential to more positive values. Asbefore, stripping the Cd layer leaves a rough Au surface behind. Themethod can be applied to any alloy system that shows alloying at theinterface (e.g. Pt-Me (Me=Ag, Pb, Sn, Hg); Au-Me (Me−Ag, Cu, Cd, Pb, Pd,Al, Hg, Sn), Ag-Me (Me=Cd, Ph).

In this example, Au nanocables array is the working electrode and theElectrochemical Adsorption-Desorption (ECAD) process is applied to theAu—Cd system. Electrochemical deposition of Cd is carried out at roomtemperature in 50 mM H₂SO₄ ⁴+1 mM CdSO₄ solution, deoxygenated withnitrogen prior to use. All potentials reported here are relative tonormal hydrogen electrode (NHE). The electrochemical deposition of Cdwas performed at various potentials in the under potential deposition(UPD) region, i.e. from −0.3 to −0.49 V for various times. Duringdeposition, the morphology of the surface does not change. Thus theformation of the alloy will not deform the bristles and will not affectthe nanostructure array. Stripping the cadmium layer by changing thepotential to 0.65 V produces to a rough surface. Depending on thedeposition conditions (in this case, potential and time), we can controlthe penetration depth of the alloy.

Tailored nanoporous metal nanostructures arrays created by the proposedmethod may also be suitable for sensor applications, particularly in abiomaterials context, catalyst and electrodes. The nanocable would becoated using the above-mentioned methods but would have at least 10× thesurface area of the initial cables. Alternatively, smooth nanocablesurfaces can be obtained by electrochemical annealing. This method hasseveral advantages. First, the electrochemical deposition of thesubsequent layers (CdTe) can be performed in the same electrochemicalcell; this eliminates the contamination during handling the sample(especially for nanostructures with huge surface area, contamination isthe most important problem).

Second, the nano-rough nanostructure is more robust because thenanoporous structure is confined to a few monolayers in the surface (notthe entire bristle volume) and still maintains a plain metallic core.

Third, the roughness of the surface can be controlled within a fewnanometers (which is in fact the surface layer for a cylinder with adiameter of 100 inn) by varying the deposition conditions so the cablecan be made rough while maintaining structural integrity.

Fourth, upon subsequent conformal deposit layers of CdTe and CdS, andfinally TCO or polymer, the porous structure is further strengthened.The final advantage is that multiple reflections (the light is trappedinto the nano-size cavity of a bristle and will have several reflectionbefore it is reflected into the neighbor bristle) increases theefficiency of light absorption.

The Cd/Au method is particularly robust.

The bristles 20 may be shaped to increase the surface area. For example,the bristles 20 may have “branches” or holes in the nanocable. Holes maybe created by depositing the Cd/Au alloy as just described andanodizing.

As another alternative to the method of FIGS. 5A-5H, the solar brush 10in be prepared using a reverse-nanocable fabrication method that isillustrated in FIGS. 6A-6F, the nanocable is formed as one of the laststeps in the reverse-fabrication method, the nanocables are preparedafter one of the conductive layers, unlike in the method of FIGS. 5A-5H.Titanium isopropoxide may be used as the precursor molecule for thesol-gel preparation of the TiO₂ nanostructures.

FIG. 6A illustrates a template membrane 60 that may be used for thereverse-fabrication method. The template membrane 60 has a substrate 62(e.g., soda lime glass). The template membrane 60 is obtained by coatingthe substrate 62 with a high-purity aluminum layer. A transparent oxidelayer is formed using a two-step anodization process: depositing on thealuminum layer, and forming porous aluminum layer columns 67.Substantially all of the high-purity aluminum layer that is coated onthe substrate is oxidized to form the aluminum layer columns 67. Thearea between the porous aluminum columns 67 are pores 64 of the templatemembrane 60. A conductive or semiconductive layer 66 is deposited on thesubstrate 62.

FIG. 6B illustrates the sol gel deposition of transparent conductiveoxide in the pores. Sol gel deposition can be performed in eitherattached or detached porous membrane. First, titanium isopropoxide isdissolved in 95% ethanol to yield a concentration of typically 20 v/v %.A second solution is then prepared by mixing 25 mL of ethanol with 0.5mL of water and 0.5 mL of 0.1 M HCl. Equal volumes of the titaniumisopropoxide solution and the second solution are then combined to yieldthe TiO₂ sol. The template membrane 60 is then dipped into this sol forthe desired amount of time, removed, and allowed to dry in air for 30min. The sol-containing membrane is then heated in air at 400° C. for 24hours. This procedure yields TiO₂ tubules or fibrils within the poresand TiO₂ films on both faces of the template membrane. Electrophoresisand centrifugation can be applied in order to obtain a densernanostructure. A transparent conductive oxide pillar 68 is formed of anyconductive oxide material or, for example, Ti with a conductive oxidematerial formed thereon by plasma vapor deposition PVD.

FIG. 6C illustrates the removal of the porous aluminum columns 67 of thetemplate membrane 60. The surface films can be removed by polishing thetemplate membrane 60 with 1500 grit sand paper or nanoscale millingusing ultrashort laser pulses or other wafer fabrication millingtechniques. If desired, the alumina template membrane 60 can then bedissolved away b immersion in aqueous base to expose the synthesizedTiO2 pillars 68.

FIG. 6D illustrates the deposition of a n-type semiconductor layer 70over the pillars 68. The n-type semiconductor layer 70 may contain CdS,which may be electrochemically deposited. CdS is also deposited on theconductive oxide layer 66 between the pillars 68.

FIG. 6E illustrates the deposition of an p-type semiconductor layer 72over the p-type semiconductor layer 70. The p-type semiconductor layer72 may contain CdTe, which may be electrochemically deposited. CdTe mayalso be deposited in the areas between the CdS layers.

FIG. 6F illustrates an electroless deposition of a metal contact 74. Themetal contact 74 fills the gaps between the CdTe layers, thereby formingthe nanocable, which in actuality may appear as a lattice. This processmay be especially beneficial for formation of Au and Cu nanocables atextremely high aspect ratios.

To create an insulating layer in between nanocables, the top metalcontact 74 can be removed to expose the composite surface made ofconductive nanowire and p layer. Then, the p layer and n layer can beselectively etched leaving the conductive nanowires sticking out the topsurface. Then, an insulating layer can be applied and the surface isthen polished to result in a composite surface made of conductivenanowires and insulating layer. Then, a conductive layer is appliedwhich will create the contact with the nanowires.

If the aspect ratio is too great, softer nanocables may collapse undertheir own weight. Tall Au or Cu nanocables may be fragile, and theirstrength may be increased by alloying Au with other metals or byreinforcing the gold with it hard metal coating. FIGS. 7A-7H illustratea hard-metal reinforcement process that may be used to strengthen thefragile nanocables. Any hard metal (such as nickel or molybdenum) thatworks at high temperatures may be used for the metal reinforcement.However, in the interest of clarity, FIGS. 7A-7H will be described usingnickel as the reinforcement metal.

As shown in FIG. 7A, the metal reinforcement process begins by providinga substrate 80. The substrate 80 is metallized by deposition of a firstconductive layer 82, as shown in FIG. 7B. Preferably, the substrate 80is of the same base metal as the nanocable core to facilitate physicallystrong junctions at the base of the cable as well as to provide goodconductivity. The first conductive layer 82 may have a height of h, asshown. The first conductive layer 82 may be, for example, 99.99% purealuminum. Then, as shown in FIG. 7C, the first conductive layer isoxidized under controlled temperature and voltage to form a metal oxideporous membrane 84 of a preselected shape having a pore 85. Since notmuch growth occurs during oxidation, the height of the metal oxideporous membrane 84 remains at approximately h. If desired, anappropriate commercial membrane may be used instead of forming, themetal oxide membrane 84

FIG. 7D shows that the metal oxide porous membrane 84 template isexposed to ethylene in an argon environment at a temperature of about650-750° C. to form carbon nanotubes 86. The exposure ma be done byplacing the “template” made of the substrate $0 and the membrane 84 in aheated chamber and adding ethylene to the chamber. Initially, the carbonlayer is formed on top of the metal oxide membrane 84 as well as on thebase and the inner walls of the pore 85. The carbon layer is, however,removed from the top of the metal oxide membrane 84 and the base of thepore 85, leaving carbon nanotube 86 as shown in FIG. 7D. Etching RIE orwet etching) or polishing may be used to remove select portions of thecarbon layer. The carbon nanotubes 86 are formed along the innersidewalls of the metal oxide membrane 84.

FIG. 7E shows nickel deposition, which may be done b electrolyticallyplating the nickel on the carbon nanotube 86. After deposition, thenickel is heated in air to 400° C. to form a nickel oxide nanotube 86.The nickel nanotube. 8 is then be filled with a core metal 90, such asgold or copper, as shown in FIG. 7F. As shown in FIG. 7G, the templateand the nanotubes are exposed to air at 600° C. to burn away the carbonnano tube. As shown, removal of the carbon nanotube 86 leaves a gap 87separating the nickel-enforced core metal 90 from the metal oxidemembrane 84. In FIG. 7H, the metal oxide membrane 84 (in this casealuminum oxide) is removed, for example by being dissolved in sodiumhydroxide A nickel enforced nanocable 88+90 remains.

If desired, the gap 87 (see FIG. 70) may be filled with a photovoltaicpolymer (e.g., an organic polymer) or titanium dioxide. The size of thegap 87, which is determined by the size of the carbon nanotube 85,controls the diameter of the nanocable that ultimately forms. Especiallyif the gap 87 will be filled with a material that forms the outermostwall of the nanocable, the size of the gap 87 is important in that itdetermines the thickness of the outermost wall.

FIG. 8 is a flowchart summarizing the steps of the hard-metalreinforcement process 92 that is schematically illustrated in FIGS.7A-7H. First, the substrate is metallized (step 94) by deposition of aconductive layer. A membrane with anodized pores is formed on themetallized substrate (step 95), and carbon nanotubes are formed on themembrane (step 98). A hard metal such as nickel is electroplated on thecarbon nanotubes (step 100) so as to form a cavity in the core. The coreis then filled with a core metal such as gold or copper (step 102) toform the nanocable. The carbon nanotube is then removed (step 104) andthe template is dissolved (step 106) to leave the metal enforcednanocable.

If the core metal is gold, which may be too soft, copper nanotube may beformed on the nickel nanotube or instead of nickel nanotube to form areinforcement for the gold nanocable.

Nanocables may also be strengthened by a more precise control of theirdimension, as shown in FIGS. 9A-9H. As in the metal reinforcementprocess of FIGS. 7A-7H, a substrate 100 is provided (FIG. 9A) andmetallized (FIG. 9B) by adding a conductive layer 102, which may be99.99% pure aluminum. An oxide template 104 having a pore 105 isproduced (FIG. 9C) by oxidizing the aluminum under controlledconditions. Substantially all of the conductive layer 102 turns into theoxide template 104. Then, as shown in FIG. 9I), a first polymer isdeposited on the surface and cured to form a first polymer thin film106. The polymer deposition (e.g., by inkjet coating) and curing may beperformed any number of times to form as man polymer thin films asdesired. In FIG. 9E, a second layer of polymer is deposited and cured toform a second polymer thin film 108.

As shown in FIG. 9F, the polymer thin films 106, 108 on the top of themembrane and the base of the pore are removed. Next, electroless orelectrochemical deposition of metal can take place inside of the pore105 (FIG. 96). A solvent extraction removes the polymer thin layers 106,108 and a NaOH extraction removes the metal oxide template 104 to leavea precisely designed nanocable (FIG. 9H). Poly filers such aspoly(3-hexylthiophene) (P3HT), poly [2-methoxy,5-(2-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV); poly (phenylenevinylene) (PPV), and polyaniline may be used as the polymer thin layers106, 108. Additionally, any suitable polymer from the Handbook ofConductive Polymers 1 I by T. A. Skathetin or the Handbook of PolymerCoatings for Electronics Chemistry by J. J. Licari and L. A. Hughes maybe used.

FIG. 10 is a flowchart summarizing the steps of the metal reinforcementprocess illustrated in FIGS. 9A-914. First, the substrate is metallized(step 112) by deposition of a conductive material on its surface. Amembrane (a template) is formed on the metallized substrate, and themembrane has a pore of the desired size and shape that is anodized (step114). One or more polymer layers are deposited and cured (step 116). Thepolymer layers on horizontal surfaces, such as the top of the templateand the base of the pore, are removed by reactive ion etching (step118). The pore is filled, with a core metal such as gold or copper (step120). Then, the polymer layers are dissolved (step 122) and the membraneis removed by solvent extraction (step 124).

FIGS. 11A-11I illustrate that organic nanocables may be produced using acarbon jacket process. FIG. 11A shows a substrate 130 with a conductivelayer 132 deposited on its surface. In the same manner as describedabove in reference to FIG. 7C, a metal oxide membrane 134 is formed,wherein the membrane has a pore 135 of the desired shape and size (FIG.11B). As shown in FIG. 11C, carbon nanotubes 136 are formed on the innerwall of the pore 135 in to manner similar to what is described above inreference to FIG. 7D, and titanium dioxide 138 is used to fill theremaining core portion of the pore 135 (FIG. 11D). As shown, titaniumdioxide 138 tills the pore 135 and “overflows” to form a cap 139 abovethe carbon nanotube 136 and the metal oxide membrane 134. The cap 139 ofthe titanium dioxide 138 is removed in FIG. 11E, for example by anysuitable etching method such as concentrated H₂SO₄ etch.

With the titanium dioxide cap 139 removed, the carbon nanotube 136 isburned off by exposure to air at about 600° C. (FIG. 11F), forming a gap140 between the titanium dioxide core 138 and the metal oxide membrane134. An organic Grätzel dye 142 is then deposited to fill the gap 140and form an organic cap 14 (FIG. 11G). Polymers such apoly(3-hexylthiophene) (P3HT),poly[2-methoxy-5-(2-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV),poly (phenylene vinylene) (PPV), and polyaniline, or any other suitablepolymers from Handbook of Conductive Polymers 1 may be used with theGrätzel dye 142 as conductors. The organic Grätzel dye 142 can besprayed with an inkjet printer, applied with a rotogravure process,sprayed on and wiped with a doctor blade, etc. The most suitableapplications leave the minimum organic cap 141. Following thispreliminary removal, the organic cap 141 may be etched (e.g., with RIE)or removed with a solvent wash to complete the removal process (FIG.11H). Then, the metal oxide membrane 134 is removed, for example by wetetching with a carefully selected etchant NaOH) that preferentiallyremoves the metal oxide over titanium dioxide (FIG. 11I), in someembodiments, the metal oxide membrane 134 is made to be transparent sothat its removal is not needed.

FIG. 12 is a flowchart summarizing the carbon jacket process illustratedin 11A-11I. As shown, a substrate surface is metallized if needed (step152). Anodized pores are formed by preparation of the metal oxidemembrane on the substrate (step 154), Then, carbon nanotubes are formedon the walls of the anodized pores (step 156), and titanium dioxide isdeposited in the remaining core portion of the pores (step 158). Artytitanium dioxide that flowed over and formed a titanium dioxide cap isremoved by etching (step 160), exposing the carbon nanotubes. The carbonnanotubes are burned away (step 162), leaving a gap between the titaniumdioxide and the metal oxide membrane. An organic polymer is deposited totill this gap (step 164), and any organic polymer that overflows andforms a cap is removed, for example by wet or dry etching (step 166).The metal oxide membrane is then dissolved with NaOH (step 168). Theresulting nanocable has a titanium dioxide core reinforced with artorganic polymer. This nanocable may be coated with a conductive polymer(step 170) that serves as the n-type conductor.

FIG. 13A shows an insulator 181 deposited on a conductor 180. Theinsulator can be any insulating material such as metal oxide, siliconedioxide, or polymer. The insulator can be applied through CVD orsputtered. It can also be anodically grown from metal deposited on theconductor 181. FIG. 13B shows how the insulator can be wet or dry etchedto form a pore that continues through to the conductor 180. FIG. 13Cshows that the conductor can then be deposited through electroplating orthe electroless deposition methods contained herein. FIG. 13 D shows theconductor partially etched. In the case of silicone dioxide, a KOHsolution can be used for etching, in the case of polymers,dichloromethane may be used. FIG. 13E shows the completed nanocable withthe p-conductor 180, the insulator 181, the p-layer 182, the n-layer183, and the TCO 184.

FIG. 14 shows the solar brush 10 encapsulated in an optical casing 40for protection from various environmental elements. The optical casing40 may also be made of a transparent polymer. The optical easing 40 maybe made of film conductive oxides that allow light in but minimize soiland moisture contamination. Common materials for this applicationinclude Sn doped Sn₂O₂, Sn doped In₂O₃, ZnSnO₃, B doped ZnO. F dopedIn₂O, F doped SnO₂, F doped Cd₂SnO₄, F doped ZnO, TIN, Ag, Cd₂SnO₄, Gedoped In₂O₃, Ge doped SnO₂, Ge doped Zn₂SnO₄, ZnO/CdS, ZnO/ZnSe (forCdTE and CuInSe₂), ZnO/In_(x)Se_(y) (for CdTE and CuInSe₂), SnO₂glass,ZnO/CdS, Cd₂SnO₄/Zn₂SnO₄, Zn(Se, OH), Zn(Se, O), and Cd₂SnO₄/Zn₂SnO₄.For additional conductivity small wires or metal strips or thin bands ofmetalized glass can be added for additional conductivity. Metal shouldbe minimized to reduce reflection but be sufficient for adequateconduction of electricity. Traditional casing of low-iron glass andextruded aluminum may also be used as in the case of created a module ofa form compatible with existing PV modules.

In some embodiments, a back contact is employed. The hack contact couldbe especially useful for hi-layered photovoltaic cells to reflect thephotons from a high hand gap materials at the top of the cell to lowband gap materials at the bottom of the cell. The reflection stillallows light have single passes through the PV material fromreflections. Where a reflective back contact is used, the opticalreflector may include Sb₂Te₃, Ni, NiTe, and Te/CdTe.

Soil build up might eventually reduce the effectiveness of the solarcell. Fluorosilicone polymers would greatly reduce soil adhesion andallow maximum cleaning during rain storms. Additionally, any thermallystable material that exhibits the Lotus effect (low surface are forparticulate adhesion) may be used to keep dust of the PV cell.

To aid the maintenance of the solar cells, an LED or liquid crystaldisplay could indicate power output of solar cell, or operations of PVcell units so that malfunctioning cells could be easily identified andreplaced. As mentioned above, there are numerous advantages of the solarbrush 10 over conventional PV cells. The solar brush 10 demonstrates ahigh thermal stability. Unlike nanoparticles, where the linear thermalexpansion coefficient increases with the reduction of the average grainsize (Cu, for instance). Cu nano-wires show a smaller thermal expansioncoefficient than that of the bulk Cu. The high thermal stability isrelated to the grain boundary structure and high aspect ratio of thenanostructure. Daisy chain connections may also combat potential thermalexpansion/contraction issues by minimizing chip size and then connectingthem opposed to having a large sheet that would have a higher potentialfor stress cracking due to thermal expansion contraction. Daisy chainsbetween cells could also add flexibility to a PV brush array. Toaccomplish this, the cells may have special interlocking mechanism toserve the dual purpose of a being a robust carrier of the film duringprocessing and to speed assembly.

Because the method describes growth of conductors on a conductive sheet,the failure rate that plagues current PV cell manufacturing will begreatly improved giving further cost/efficiency advantages.

A further advantage of the PV brush is that the distance electronsdiffuse through the semiconductive layer to the conductive layer isshorter than that of conventional PV cells thereby reducing internalresistance of the PV cells to deliver further power generationefficiencies. Because the PV bristles are thin, they use a smallfraction of the material required for planar cells. A variety of organicand inorganic semiconductors can be applied to the conductive core andthicknesses can easily be optimized for power generation and stability.

Besides solar panels, nanoelectronic assemblies can also be used forlight generation in optical chips. Optical chips are widely thought tobe the replacement for semiconductor chips. Optical chips have narrowpathways that light can travel unhindered while semiconductor chips arelimited by electric field effects between on circuit and the next. Amicro light source with unique color attributes could be essential foroptical chip technologies. The nanoelectric assemblies can also be usedas a nanolight source for such chips. Additionally, the nanodiodes canbe used in a flat screen display for an ultra sharp video monitor.Additionally, the nanodiodes can be used for very energy efficientlighting.

The PV brush has flexible manufacturing, options including membranemanufacturing technologies or photolithography e-beam, low densitylayered mechanical scoring, nanoporous templated, electroplating, andelectrical arcing. These manufacturing methods can be used on a varietyof membrane/nanoporous media which allows cell to be shaped and hardenedto geometry that has maximum solar efficiency, maximum aerodynamicefficiency, maximum aesthetic appeal or a combination of theaforementioned attributes. Flexible units can also be achieved by daisychain connection between small rigid units or from the use of a flexiblesubstrate. At high temperatures, uneven thermal expansion can causecracking and wear as well. High temperature degradation is mitigatedbecause each component of this PV cell can be sized to minimize thermalexpansion and can be further optimized with flexible expansion joinconductive connections between PV arrays. Additionally, the greatersurface area of the solar brush will reduce thermal heat generated underthe PV solar cell compared to the conventional flat unit which couldgreatly reduce unwanted heat buildup. One further advantage is thatmicro conductors often have reduced resistance at higher temperatures;therefore, the PV brush could be able to transfer energy moreeffectively than conventional PV cells at higher operating temperatures.

Finally, the geometry can be used to trap or release heat. If heat werefound to be detrimental to energy above a certain point, the unit couldbe designed with vents. However, it should be noted that performance ofnanocables may be different that than large scale wires. While largescale wires/cables have higher resistance to electrical flow at hightemperatures, energy flow may improve due to improved flow through grainboundaries in nano-scale structures.

Power generation is a function of average power per day. The median sunhours for various cities in California is 6.18 kW/(day*m) according to aGo Solar® Company web page at www.solarexpert.com/Pvinsolation.html. Onaverage, solar energy is drawn from about 6 hours per day based on thedata made publicly available by National Renewable Energy laboratoryfindings. The distribution is commonly given as a Gaussian curve, whichhas the following distribution:

${f(x)} = \frac{e^{(\frac{- {({x - \mu})}^{2}}{2\sigma})}}{\sigma \sqrt{2\pi}}$

Assuming an average of μ=6 hours, a standard deviation of σ=1 hour, andintegrated power of 6.18 kwh/m² for an average day gives a maximumenergy. When x=μ, the theoretical maximum power generated is about 4.933kWhr/m². Based on EU studies of layering, the importance of having eachsolar event near the p-n junction, and reduced hot spots, the CdTesystem may approach its theoretical efficiency limit. Efficiency couldget as high as 30% with the single layer systems and potentially higherif we combined a high and low band gap system (discussed earlier). Thedistributions are shown in FIG. 15.

The power calculation works out as follows

P=6.18 kWh/(m²×d)

from the mean values for a California city

P _(Brush) =P×E×O

Thus, where E=29 (29% efficiency) for a CdTe/CdS PV cell and O=theorientation am 1.44 (44% gain), P_(Brush)=2.60 kWhr/(m²×d) (average dayin the mean city in CA). However, it should be noted that the brush canpick up about a 44.8% gain in efficiency by because it would requirelittle if any sun orientation adjustments. The orientation of the solarbrush 10 may have a large effect on performance. Planar PV modules loseup to 44% power from poor orientation and often need to be reorientedusing a “solar compass”. Due to its unique design, the solar brush 10does not require reorientation.

If electrical current through the PV device is sufficiently high, acooling systems that could either be used to generated thermoelectricpower (i.e. steam turbine type of power generation) or water beatingsystems for home use could also be possible.

A majority of the light from the sun is scattered from the atmosphere.Collecting scattered light using the solar brush 10 should lead to evenhigher energy production. Further energy gains from multi-junction solarcells may hump the efficiency to double what is believed to be currentlypossible.

The solar brush 10 will probably approach the theoretical maximumefficiency for a given material. Because the brush can be made nearlytransparent, most of the light continues to travel through the cell. Forpractical purposes, the brush would appear to be of ∞ thickness. Becausethe bristles can be designed just thick enough for stable solarabsorption, each absorptive event would happen near the p-n junction.The occurrence of the absorptive event near the p-n junction improvescell efficiency. Another key to improving cell efficiency is to reducelocalized heating. Each time there is solar absorption, part of theenergy ejects the electron and part of the energy heats the cell. Theheating reduces the efficiency of the cell. When cells rely on hackreflection, they are also doubling the heat load for a given areas. Asthe sun moves across the sky, the penetration angle is changing and thetrajectory of the solar stream is changing so there is a greaterquantity of “fresh” material for the photons to impact. With the solarbrush 10, more of the absorption events can be made to occur near thep-n junction through control of the layer thicknesses, and the lightstream will pass through greater amounts of PV material. Multiplejunction material is believed to be the key to maximum efficiency in thefuture. Table 5 shows efficiency potential, band gap, and fieldefficiencies for several materials.

TABLE 5 Efficiencies of photovoltaic material Theoretical LaboratoryField Band Maximum Maximum Efficiency Gap Material Efficiency (%)Efficiency (%) (%) (eV) Single Crystal SI 27 23.5 14.0-17.0 1.1 Si HITsingle 27 21.0 15.5-16.5 1.1 crystal Si Poly Crystal 27 20.0 11.5-14.21.1 Si Ribbon 27 17 11.0-13.0 1.1 CIS 24 18  9.0-11.5 0.9 GaAs 30 1.4CdTe 29 17  8.0-10.0 1.5 Amorphous Si 25 13.0 5.0-9.5 1.7 Indium Gallium 31* 17  8.5-11.05 0.8 Nitride Graetzel  20* 10.9 45 Polymer  9* 4.91.0-2.5 *indicates that the value is an estimate.Efficiency compares favorably with current technologies to give themaximum power increases. Table 6 shows the potential energy efficiencyand power generation capability in the state of California.

TABLE 6 Potential energy efficiency and power generation in CaliforniaMaterial Efficiency kW*hr/Day/m² PV Brush (CdTe) ~29 2.60 Single CrystalSi 17 1.19 Polymer 2.0 0.11

Power generation and effective areas for the brush can be significantlyboosted through the use of a solar concentrator. A solar concentratorcould redirect large areas of light perpendicular to the surface,thereby utilizing the surface area at the depths of the brush. Onlylight angles close to 90 can penetrate a high area shell. Thepenetration depth in shown by FIG. 1 is the spacing distance betweenbristles times tan Θ. As Θ approaches 90°, tan Θ approaches ∞ and therequired penetration level is achieved. The effective area of the solarcell is calculated by adding the penetration dept by the bristle heightand multiplying it by the area. The power output of a high efficiency,high area solar cell in one embodiment is between 50 and 285 kW/day/m²with a solar concentrator. The output ranges compare favorably with themaximum output of 0.94 kW/day/m² based on the best known field resultsever for single silicon PV arrays that are produced with a process whichis probably much more costly than the methods and structures presentedherein.

Konarka uses a technology where printed polymers generate energy fromall visible spectra. As described in http://www.konarkatech.com/about/,PV polymers are printed on polymer sheets. Materials are produced byinjecting a dye into titanium dioxide and printing the material on topolymers. The Konarka technology is expected to yield 10% efficiency andlast about 8 years. In comparison, the materials disclosed herein thatare used for the solar brush 10 have a lifespan in the 25 to 30 yeartime frame. Konarka's process may be IOU times less expensive than thesolar brush 10 but produces PV cells of only around 2% efficiency.Furthermore, these PV cells would not have a form that is compatiblewith concentrators. Therefore, the maximum power Konarka's PV film wouldexpect to generate on a given day would be about 0.11 kW/m, and thebrush could generate between 450 and 2.500 times the power that theKonarka system generates.

Table 7 illustrates the power generation for 8″ disk PV cells. Referenceis made to Table 3, above, for definitions of column headings.

TABLE 7 High efficiency solar cell power generation for 8″ disk PVcells. Estimated High Efficiency Bristle Bristle Cable Power HeightDiameter Density Area Generation (μm) (nm) (#/m²) (m²/m² planar)(kWhr/m²*day) 50 220 5 × 10¹² 172.76 48.06 100 220 5 × 10¹² 345.52 96.1250 370 1 × 10¹² 50.26 13.98 100 370 1 × 10¹² 100.54 27.96

Solar brushes 10 may be made from disks of 11″ diameter, or can be grownfrom any dimension films using oxide templates. They can use existingphotolithography and sputtering machines. If an 8″ diameter disk isused, it would generate the power equivalent of 0.97 to 5.58 m² planarphotovoltaic cells. If a perfect reflector were used in the solarcollector, the minimum dish size would range from a diameter of 1.1 m to14.8 in for full utilization of the PV cell area. Because perfectreflectors do not exist, some of the energy would be lost to absorptionand misdirected reflections, A 2 to 2.5 in diameter may be used togenerate the maximum energy. Smaller units can be produced if desired,the size being a function of the power requirements and the installationlocation. The 8″ disk could generate 1.6 to 24.42 kW/day depending onthe final area and thickness of material on a disk. The system is alsopreferably sized to allow proper current conduction without undue systemheating of the substrate metal.

The small disk size will allow easy cleaning and reduce efficiencylosses over time. Since the area of the central disk is so small, it maybe designed to snap in and out to be cleaned in a way that isimpractical for larger cells.

The wide range of methods to form nanocables on either flexible or rigidsubstrate that is shaped to a given specification then hardened impactsthe efficiency of the film.

Hard coatings such as TiN, ZrN, or HfN that have melting points around3,000° C. may be used for certain layers to minimize reflectance or as areinforcement “jacket” to increase the hardness of the nanocables.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1-36. (canceled)
 37. A photovoltaic structure, comprising: an array ofphotovoltaic nanostructures; and a photovoltaic device, the photovoltaicdevice being at least semi-transparent, wherein the array is positionedrelative to the photovoltaic device such that light passing through thephotovoltaic device strikes the array.
 38. The photovoltaic structure asrecited in claim 37, wherein the array of photovoltaic nanostructures isarranged in a brush configuration.
 39. The photovoltaic structure asrecited in claim 37, wherein axes of the photovoltaic nanostructures aretilted from a direction normal to a plane of the array.
 40. Thephotovoltaic structure as recited in claim 37, wherein the photovoltaicdevice is formed of planar photovoltaic layers.
 41. The photovoltaicstructure as recited in claim 37, wherein the photovoltaic device is asecond array of photovoltaic nanostructures.
 42. The photovoltaicstructure as recited in claim 41, wherein the first and second arrays ofphotovoltaic nanostructures are arranged in a brush configuration,wherein a height of the photovoltaic nanostructures in the first arrayis different than an average height of the photovoltaic nanostructuresin the second array.
 43. The photovoltaic structure as recited in claim41, wherein the photovoltaic nanostructures of the first array have thesame composition as the photovoltaic nanostructures of the second array.44. The photovoltaic structure as recited in claim 41, wherein thephotovoltaic nanostructures of the first array have a differentcomposition than the photovoltaic nanostructures of the second array.45. The photovoltaic structure as recited in claim 44, wherein thephotovoltaic nanostructures of the first array comprise an organicmaterial, wherein the photovoltaic nanostructures of the second arraycomprise inorganic materials.
 46. The photovoltaic structure as recitedin claim 44, wherein the photovoltaic nanostructures of the first arraycomprise inorganic materials, wherein the photovoltaic nanostructures ofthe second array comprise inorganic materials.
 47. The photovoltaicstructure as recited in claim 41, wherein the nanostructures of thesecond array are coated with at least one high bandgap material, and thenanostructures of the first array are coated with at least one lowbandgap material.
 48. The photovoltaic structure as recited in claim 37,wherein the array of photovoltaic nanostructures is encapsulated in asubstantially transparent optical casing.
 49. The photovoltaic structureas recited in claim 37, wherein the array of photovoltaic nanostructuresis divided into a plurality of cells, the cells being interconnected bydaisy chain connections.
 50. A photovoltaic structure, comprising: afirst array of photovoltaic nanostructures as recited in claim 81; and asecond array of photovoltaic nanostructures positioned relative to thefirst array such that light passing through the second array strikes thefirst array.
 51. The photovoltaic structure as recited in claim 50,wherein the first and second arrays of photovoltaic nanostructures arearranged in a brush configuration, wherein a height of the photovoltaicnanostructures in the first array is different than an average height ofthe photovoltaic nanostructures in the second array.
 52. Thephotovoltaic structure as recited in claim 50, wherein the photovoltaicnanostructures of the first array have a different composition than thephotovoltaic nanostructures of the second array.
 53. The photovoltaicstructure as recited in claim 52, wherein the photovoltaicnanostructures of the first array comprise an organic material, whereinthe photovoltaic nanostructures of the second array comprise inorganicmaterials.
 54. The photovoltaic structure as recited in claim 52,wherein the photovoltaic nanostructures of the first array compriseinorganic materials, wherein the photovoltaic nanostructures of thesecond array comprise inorganic materials.
 55. The photovoltaicstructure as recited in claim 50, wherein the nanostructures of thesecond array are coated with at least one high bandgap material, and thenanostructures of the first array are coated with at least one lowbandgap material.
 56. The photovoltaic structure as recited in claim 50,wherein each array of photovoltaic nanostructures is arranged in a brushconfiguration, wherein heights of the photovoltaic nanostructures in thefirst array are different than heights of the photovoltaicnanostructures in the second array.
 57. The photovoltaic structure asrecited in claim 50, wherein axes of the photovoltaic nanostructures ineach array are tilted from a direction normal to a plane of the array.58. The photovoltaic structure as recited in claim 50, wherein at leastone of the arrays of photovoltaic nanostructures is encapsulated in asubstantially transparent optical casing.
 59. The photovoltaic structureas recited in claim 50, wherein the arrays of photovoltaicnanostructures are divided into a plurality of cells, the cells beinginterconnected by daisy chain connections.
 60. A photovoltaic structure,comprising: multiple arrays of photovoltaic nanostructures arranged in astacked configuration, wherein at least some of the light striking afirst of the arrays passes through the first array and contacts thearray or arrays below the first army, wherein a material coating thefirst array has a relatively higher bandgap than a material coating alast array, wherein a material coating an array between the first arrayand the last array has a relatively lower bandgap than the materialcoating the first array and a relatively higher bandgap than thematerial coating the last array.
 61. A method for forming a photovoltaicstructure, comprising: coupling a photovoltaic device to an array ofphotovoltaic nanostructures, the photovoltaic device being at leastsemi-transparent, wherein the array is positioned relative to thephotovoltaic device such that light passing through the photovoltaicdevice strikes the array.
 62. The method as recited in claim 61, whereinthe array of photovoltaic nanostructures is arranged in a brushconfiguration.
 63. (canceled)
 64. (canceled)
 65. (canceled) 66.(canceled)
 67. (canceled)
 68. (canceled)
 69. (canceled)
 70. (canceled)71. (canceled)
 72. A method for forming a photovoltaic structure,comprising: coupling a first array of photovoltaic nanostructures asrecited in claim 81 to a second array of photovoltaic nanostructures,the second array of photovoltaic nanostructures being positionedrelative to the first array such that light passing through the secondarray strikes the first array.
 73. The method as recited in claim 72,wherein the first and second arrays of photovoltaic nanostructures arearranged in a brush configuration, wherein a height of the photovoltaicnanostructures in the first array is different than an average height ofthe photovoltaic nanostructures in the second array.
 74. The method asrecited in claim 72, wherein the photovoltaic nanostructures of thefirst array have the same composition as the photovoltaic nanostructuresof the second array.
 75. The method as recited in claim 72, wherein thephotovoltaic nanostructures of the first array have a differentcomposition than the photovoltaic nanostructures of the second array.76. The method as recited in claim 75, wherein the photovoltaicnanostructures of the first array comprise an organic material, whereinthe photovoltaic nanostructures of the second array comprise inorganicmaterials.
 77. The method as recited in claim 75, wherein thephotovoltaic nanostructures of the first array comprise inorganicmaterials, wherein the photovoltaic nanostructures of the second arraycomprise inorganic materials.
 78. The method as recited in claim 72,wherein the nanostructures of the second array are coated with at leastone high bandgap material, and the nanostructures of the first array arecoated with at least one low bandgap material.
 79. The method as recitedin claim 72, wherein each array of photovoltaic nanostructures isarranged in a brush configuration.
 80. The method as recited in claim72, wherein axes of the photovoltaic nanostructures in each array aretilted from a direction normal to a plane of the array.
 81. A structure,comprising: an array of nanostructures extending upwardly from asubstrate and having free ends positioned away from the substrate, eachof the nanostructures having an electrically conductive metallicnanocable therein, the nanocables being characterized as having aspacing and surface texture defined by inner surfaces of pores of atemplate, wherein longitudinal axes of the nanocables are orientedparallel to each other; and each of the nanostructures also having atleast one layer overlaying the nanocable thereof, wherein the at leastone layer creates a photovoltaically active p-n junction in an interiorof the respective nanostructure, wherein a gap is present between outersurfaces of the nanostructures.
 82. The structure as recited in claim81, wherein the nanocables and the at least one layer overlying thenanocables form bristles, wherein no solid fill material is presentbetween upper portions of the bristles, wherein the bristles haverounded cross sectional peripheries taken perpendicular to longitudinalaxes of the bristles.
 83. The structure as recited in claim 81, whereinthe template is partially removed from an area adjacent portions of thenanocables thereby exposing the portions of the nanocables above aportion of the template that remains including free ends of thenanocables, wherein a thickness of the template that remains is lessthan a thickness of the array of nanocables, said thicknesses beingmeasured in a direction perpendicular to a plane of the substrate. 84.The structure as recited in claim 83, further comprising an electricallyinsulating layer extending along the substrate, wherein at least aportion of the insulating layer is the template.
 85. The structure asrecited in claim 81, wherein the nanocables have substantially uniformperipheries.
 86. The structure as recited in claim 81, wherein thenanocables in the array are characterized as having a spacing andsurface texture defined by inner surfaces of voids of a membranetemplate.
 87. The structure as recited in claim 81, wherein the at leastone layer is an electroplated layer.
 88. The structure as recited inclaim 81, wherein the at least one layer has a physical structurecharacterized by formation by chemical vapor deposition and etching. 89.The nanostructure as recited in claim 81, wherein the nanostructures areelongate, wherein axes of the nanostructures are tilted from a directionnormal to a plane of the substrate.
 90. The structure as recited inclaim 81, further comprising an optical casing filling in the gapbetween the nanostructures.
 91. A structure, comprising: a substrate; anarray of nanocables extending from the substrate, portions of thenanocables being characterized as having a spacing, shape and surfacetexture defined by previously-present inner surfaces of pores of atemplate that has been at least partially removed, wherein thepreviously-present inner surfaces of the pores of the template are notpresent adjacent the portions of the nanocables; an electricallyinsulating layer extending along the substrate in a gap between thenanocables; and at least one layer overlaying the nanocables.
 92. Thestructure as recited in claim 91, further comprising a portion of thetemplate extending along the substrate, the portion of the templatehaving a thickness that is less than a previous thickness thereof at atime when the nanocables were formed therein, said thickness beingmeasured in a direction perpendicular to a plane of the substrate, thetemplate being electrically insulative.
 93. The structure as recited inclaim 92, wherein a thickness of the template is less than alongitudinal length of the nanocables.
 94. The structure as recited inclaim 93, wherein a remaining portion of the template is the insulatinglayer.
 95. The structure as recited in claim 91, wherein the nanocableshave substantially uniform peripheries, the nanocables having roundedcross sectional peripheries taken perpendicular to longitudinal axesthereof.
 96. The structure as recited in claim 91, wherein the templateis a membrane.
 97. The structure as recited in claim 91, wherein the atleast one layer is an electroplated layer.
 98. The structure as recitedin claim 91, wherein the at least one layer has a physical structurecharacterized by formation by chemical vapor deposition and etching. 99.The nanostructure as recited in claim 91, wherein the nanostructures areelongate, wherein axes of the nanostructures are tilted from a directionnormal to a plane of the substrate.
 100. The structure as recited inclaim 91, wherein the at least one layer creates a photovoltaicallyactive p-n junction.
 101. A method for creating a nanostructure,comprising: depositing material in a template for forming an array ofnanocables; removing only a portion of the template such that thetemplate forms an insulating layer between the nanocables; and formingat least one layer over the nanocables.
 102. The method as recited inclaim 101, wherein the at least one layer is formed by electroplating.103. The method as recited in claim 101, wherein the at least one layercreates a photovoltaically active p-n junction.
 104. The method asrecited in claim 101, wherein the at least one layer is formed bychemical vapor deposition.
 105. The method as recited in claim 101,wherein forming the at least one layer over the nanocables includessputtering a layer of CIS, CIGS, or CdTe/CdS over the nanocables.
 106. Amethod for creating a nanostructure, comprising: depositing material ina template for forming an array of nanocables; removing the template;forming an insulating layer between the nanocables; and forming at leastone layer over the nanocables.
 107. The method as recited in claim 106,wherein the at least one layer is formed by electroplating.
 108. Themethod as recited in claim 106, wherein the at least one layer is formedby chemical vapor deposition, and further comprising the step of etchingto expose the insulating layer.
 109. The method as recited in claim 106,wherein the at least one layer creates a photovoltaically active p-njunction.
 110. The method as recited in claim 106, wherein forming theat least one layer over the nanocables includes sputtering a layer ofCIS, CIGS, or CdTe/CdS over the nanocables.
 111. A method for creating ananostructure, comprising: depositing material in a template for formingan array of pillars; removing the template; forming at least one layerover the pillars such that the pillars are covered by the at least onelayer; and depositing a metal contact over the at least one layer suchthat the at least one layer is covered by the metal contact.
 112. Themethod as recited in claim 111, further comprising applying a templatematerial to a substrate, and selectively removing portions of thematerial for creating the template.
 113. The method as recited in claim112, wherein the template material is initially a substantially puremetal, wherein the selectively removing portions of the materialincludes oxidizing the substantially pure metal.
 114. The method asrecited in claim 111, wherein the material is deposited in the templateusing sol gel deposition.
 115. The method as recited in claim 111,wherein the at least one layer creates a photovoltaically active p-njunction.
 116. The method as recited in claim 111, wherein forming theat least one layer over the pillars includes sputtering a layer of CIS,CIGS, or CdTe/CdS over the pillars.
 117. A nanostructure, comprising: ananocable having a roughened outer surface and a solid core.
 118. Thenanostructure as recited in claim 117, wherein the roughened outersurface includes pores.
 119. The nanostructure as recited in claim 117,wherein the roughened outer surface includes cavities.
 120. Thenanostructure as recited in claim 117, wherein the core is formed of ametal.
 121. The nanostructure as recited in claim 120, wherein the coreis selected from a group consisting of gold, silver and platinum. 122.The nanostructure as recited in claim 117, wherein the nanocable has asurface area that is at least ten times an outer surface area of asmooth solid cylinder having identical average dimensions as thenanocable.
 123. The nanostructure as recited in claim 117, furthercomprising at least one layer formed over the roughened outer surface,the at least one layer creating a photovoltaically active p-n junction.124. The nanostructure as recited in claim 123, wherein the roughenedouter surface is reflective.
 125. A nanostructure, comprising: an arrayof nanocables each having a roughened outer surface and a solid core,the roughened outer surface including reflective cavities; and at leastone layer formed over the roughened outer surfaces of the nanocables,the at least one layer creating a photovoltaically active p-n junction.126. The nanostructure as recited in claim 125, wherein the core isformed of a metal.
 127. The nanostructure as recited in claim 126,wherein the core is selected from a group consisting of gold, silver andplatinum.
 128. The nanostructure as recited in claim 125, wherein eachnanocable has a surface area that is at least ten times an outer surfacearea of a smooth solid cylinder having identical average dimensions asthe nanocable.
 129. A method for creating a nanocable with a rough outersurface, comprising: plating a metal over the surface of a metallicnanocable such that the metal forms an alloy with the nanocable at thesurface of the nanocable; and removing the metal from the surface of thenanocable, wherein the outer surface of the nanocable is rough uponremoval of the metal.
 130. The method as recited in claim 129, whereinthe metal is plated at a potential in an under-potential depositionregion, wherein the metal is removed at least in part by switching thepotential to a relatively more positive value.
 131. The method asrecited in claim 129, wherein the metal is removed at least in part byexposure to a corrosive material.
 132. The method as recited in claim129, wherein the roughened outer surface includes pores.
 133. The methodas recited in claim 129, wherein the roughened outer surface includescavities.
 134. The method as recited in claim 129, wherein the nanocableis formed of a material selected from a group consisting of gold, silverand platinum.
 135. The method as recited in claim 129, wherein thesurface area of the nanocable after removing the metal is at least tentimes an outer surface area of the nanocable prior to plating the metal.136. The method as recited in claim 129, further comprising forming atleast one layer over the rough outer surface, the at least one layercreating a photovoltaically active p-n junction.
 137. The method asrecited in claim 136, wherein the roughened outer surface is reflective.138. A method for creating a nanostructure, comprising: plating a metalover the surface of a metallic nanocable such that the metal forms analloy with the nanocable at the surface of the nanocable; removing themetal from the surface of the nanocable, wherein the outer surface ofthe nanocable is rough upon removal of the metal, wherein the roughenedouter surface includes at least one of pores and cavities; forming atleast one layer over the rough outer surface, the at least one layercreating a photovoltaically active p-n junction.
 139. (canceled) 140.(canceled)
 141. (canceled)
 142. A reinforced structure, comprising: ananotube of a first material; a nanocable of a second material in thenanotube, wherein the first material is more rigid than the secondmaterial; and a pair of layers over the nanotube, the pair of layersforming a photovoltaically active p-n junction.
 143. The reinforcedstructure as recited in claim 142, wherein the first material has ahigher heat resistance than the second material.
 144. A method forcreating a reinforced nanostructure, comprising: forming a nanotube of afirst material in a template; and forming a nanocable of a secondmaterial in the nanotube.
 145. (canceled)
 146. (canceled) 147.(canceled)
 148. (canceled)
 149. (canceled)
 150. (canceled) 151.(canceled)
 152. (canceled)
 153. (canceled)
 154. (canceled)
 155. A methodfor creating a reinforced nanostructure, comprising: forming a nanotubeof a first material in a template; forming a nanocable of a secondmaterial in the nanotube; removing the nanotube from between thetemplate and the nanocable; and depositing a reinforcing layer betweenthe template and the nanocable.
 156. The method as recited in claim 155,wherein the reinforcing layer is formed of a material that is more rigidthan the second material.
 157. The method as recited in claim 155,wherein the reinforcing layer is formed of a material that has a higherheat resistance than the second material.
 158. The method as recited inclaim 155, wherein the reinforcing layer is formed of an organicmaterial.
 159. The method as recited in claim 155, further comprising atleast partially removing the template.
 160. A method for creating ananocable through etching a membrane on a conductor comprising:depositing material in a template for forming an array of nanocables;removing the template; forming an insulating layer between thenanocables; and forming at least one layer over the nanocables.
 161. Amethod for creating an array of nanocables having a defined dimensionperpendicular to an axis thereof, comprising: forming a nanotube of apolymeric material in a template; and forming a nanocable of a secondmaterial in the nanotube.
 162. The method as recited in claim 161,wherein the nanotube comprises at least two layers of polymericmaterial.
 163. The method as recited in claim 161, wherein forming thenanotube includes depositing multiple layers of polymeric material fordefining an outer dimension of the nanocable.
 164. (canceled)
 165. Themethod as recited in claim 161, further comprising at least partiallyremoving the template.
 166. A method for creating an array of nanocableshaving a defined dimension perpendicular to an axis thereof, comprising:determining a desired dimension of a nanocable in a directionperpendicular to an axis thereof; depositing multiple layers ofpolymeric material onto surfaces of pores of a template thereby forminga nanotube having an inner surface defining a void of about the desireddimension of the nanocable; and forming a nanocable of a second materialin the nanotube.
 167. The method as recited in claim 166, furthercomprising removing at least a portion of the polymeric material. 168.The method as recited in claim 166, further comprising at leastpartially removing the template.
 169. The structure as recited in claim81, wherein each of the nanocables is an electroplated member. 170.(canceled)
 171. The structure as recited in claim 81, whereinthicknesses of the nanocables measured along longitudinal axes thereofare about the same.
 172. The structure as recited in claim 81, whereineach of the nanocables has about a constant cross sectional diameteralong a longitudinal length thereof.
 173. The structure as recited inclaim 91, wherein the nanocables and the at least one layer overlyingthe nanocables form bristles, wherein no solid fill material is presentbetween upper portions of the bristles.
 174. The structure as recited inclaim 91, wherein longitudinal axes of the nanocables are orientedparallel to each other.
 175. The structure as recited in claim 91,wherein each of the nanocables is an electroplated member.
 176. Thestructure as recited in claim 91, wherein thicknesses of the nanocablesmeasured along longitudinal axes thereof are about the same.
 177. Thestructure as recited in claim 91, wherein each of the nanocables hasabout a constant cross sectional diameter along a longitudinal lengththereof.
 178. The structure as recited in claim 142, wherein thenanocable is electrically conductive.
 179. The structure as recited inclaim 178, further comprising an array of the nanotubes having thenanocables therein and the pair of layers thereover extending from acommon substrate, the nanotubes having longitudinal axes orientedparallel to one another.
 180. The structure as recited in claim 81,wherein the free ends of the nanostructures are opposite to ends of thenanostructures closest to the substrate.
 181. The structure as recitedin claim 81, wherein the at least one layer creating thephotovoltaically active p-n junction in the interior of the respectivenanostructure overlays outside surfaces and the free ends of thenanocables.
 182. The structure as recited in claim 83, wherein the atleast one layer creating the photovoltaically active p-n junction in theinterior of the respective nanostructure overlays outside surfaces ofthe exposed portions of the nanocables above the remaining portion ofthe template, the at least one layer extending along the outsidesurfaces of the exposed portions of the nanocables from the remainingportion of the template to the free ends of the nanocables.
 183. Thestructure as recited in claim 81, wherein the template extends onlyalong lower portions of the nanocables, the individual free ends of thenanostructures protruding above the template.
 184. The structure asrecited in claim 183, wherein upper portions of the nanocables above thetemplate are characterized as having a spacing, shape and surfacetexture defined by pores of a previously-present portion of the templatethat defined the upper portions of the nanocables.
 185. The structure asrecited in claim 81, wherein the nanocables are nanorods or fillednanotubes, over which the at least one layer is formed.
 186. Thestructure as recited in claim 81, wherein the template is not present inthe structure.
 187. The structure as recited in claim 91, wherein thetemplate is not present in the structure.
 188. The structure as recitedin claim 91, wherein the template is no longer present or only partiallyremains and extends along the nanocables to a point on each nanocablebelow the upper portion of the nanocable.
 189. A structure, comprising:a substrate; an array of nanocables extending from the substrate, upperportions of the nanocables being characterized as having a spacing,shape and surface texture defined by pores of a template that is nolonger present or that only partially remains and extends along thenanocables to a point on each nanocable below the upper portion of thenanocable; an electrically insulating layer extending along thesubstrate in a gap between the nanocables; and at least one layeroverlaying the nanocables, thereby forming an array of bristles, whereinthe at least one layer creates a photovoltaically active p-n junction ineach of the bristles, wherein each of the bristles has a free endopposite an end of the bristle closest to the substrate, wherein a gapis present between the free ends of the bristles.
 190. The structure asrecited in claim 189, further comprising an optical casing in the gapbetween the free ends of the bristles.
 191. The structure as recited inclaim 190, wherein the optical casing also covers tops of the free endsof the bristles, thereby encapsulating the free ends of the bristles.192. The structure as recited in claim 189, wherein the at least onelayer overlaying the nanocables includes a layer of CIS, CIGS, and/orCdTe/CdS.
 193. The structure as recited in claim 189, wherein the atleast one layer overlaying the nanocables includes amorphous silicon.194. The structure as recited in claim 189, wherein the nanocablesinclude amorphous silicon.
 195. The structure as recited in claim 81,wherein the at least one layer overlaying the nanocable includes a layerof CIS, CIGS, and/or CdTe/CdS.
 196. The structure as recited in claim81, wherein the at least one layer overlaying the nanocable includesamorphous silicon.
 197. The structure as recited in claim 81, whereinthe nanostructures include amorphous silicon.
 198. The structure asrecited in claim 91, wherein the at least one layer overlaying thenanocables includes a layer of CIS, CIGS, and/or CdTe/CdS.
 199. Thestructure as recited in claim 91, wherein the at least one layeroverlaying the nanocables includes amorphous silicon.
 200. The structureas recited in claim 91, wherein the nanocables include amorphoussilicon.
 201. The reinforced structure as recited in claim 142, whereinat least one layer of the pair of layers includes a layer of CIS, CIGS,and/or CdTe/CdS.
 202. The reinforced structure as recited in claim 142,wherein at least one layer of the pair of layers includes a layer ofamorphous silicon.
 203. The reinforced structure as recited in claim142, wherein the second material includes amorphous silicon.